Carefully lifting the vial out of his package, Jon felt himself take a deep breath, nervous about the effects of drinking it. It had not been the first time since he’d had to use such a chemical concoction, perhaps one of the better parts of the course he had signed up for. But this time…as much as he knew it was part of the study, and he would likely have to change this way at some point in the semester, now that the time was here, Jon found himself rather nervous. 

Across the table was his friend and roommate Matt, taking his own vial with a bit more enthusiasm. He didn’t seem to carry the same sense of trepidation as Jon did, and Jon had respect for that. At least they would be working on this project at the same time, but that was only a small consolation when the change he was about to undergo was so drastic, at least by his metrics. 

“Hell of a way to spend a weekend, eh?” Matt remarked, clearly eager to take the sip from his vial. They had decided they would take it at the same time, but Jon began to feel he would need a push in order to start the process. The uniqueness of this change was enough that he couldn’t see himself going into it headfirst, and found himself hoping the pleasures of the change would outweigh his initial hesitation. 

“I mean, it could be worse…” Jon commented, looking down at the vial in his hand with a bit of a shudder. “We might have to get fucked afterward, right?”

“Or better, if you’re into that,” Matt said with a grin. In addition to being roommates, Matt and Jon had been friends within their program all term. Jon knew how much Matt loved the transformations and the sexual acts that often accompanied them. Not that Jon was prudish, or any of the like. In fact, Matt’s interest had been the final push Jon needed to try things he was otherwise nervous to do. But in this case, the notion that they would not only be turning into animals but to swap genders was more nerve-wracking than any change thus far. And to remain in those forms for the weekend, no less!

Both Jon and Matt were part of a two-year specialty program at their universities’ post-zoological studies. There were only a handful of people who qualified for this program, one designed to expose students to a variety of animal bodies via means of nanite transformation. It was a relatively new field of study, one that prepared students for long-term studies on animal behavior and physiology by becoming them and experiencing things from a human perspective. As part of those studies, the students were required to take on a variety of forms from different animal phyla in order to become familiar with the technology. For Jon, it had been amazing, even some of the more daunting tasks that came with consensual mating and courtship activities. They were something the students had to sign disclosure agreements to keep things reasonable from a sexual and consent perspective. But this was the first time the course required him to change gender, a randomly assigned female animal with the option to be paired and bred with a classmate who had become male. And that wasn’t even the most extreme option that was on the table…

“I can’t believe there was extra credit involved for anyone choosing to become pregnant!” Jon exclaimed, as though such was something no one would consider. The process would inseminate the participant and force them through a rapid pregnancy, one that would come to term after an extra couple of days remaining in their animal form. It was less about remaining in a pregnant state and more about reflecting on the birthing process itself. Still, it was something Jon figured was too extreme for him to even fathom. Not that his grades were the best, but he didn’t need the extra credit that badly!

“Yeah, about that…” Matt remarked, a mischievous look in his eye. Almost as though he had…

“You didn’t!?” Jon exclaimed, totally surprised not only that his roommate would do that, but seemed excited about it. Still, if any of the other guys in the class would take the challenge for extra credit, it would be Matt. 

“I mean, it is for extra credit…” Matt remarked, though he hardly needed it. Jon was sure he was doing it for the experience, and in the end, he figured he was in no place to judge, happy for Matt if he was this excited. 

“So, what did you get assigned?” Jon asked, changing the subject. They had just found out the day before, and the two of them hadn’t had the chance to talk about it yet. 

“A horse! Well, a mare, I suppose. Hell, I haven’t had a chance to be a horse yet, and I’ve always wanted to be a-well, maybe not a mare, but I’m sure it will be fine. How about you?”

“Oh! A lioness,” Jon replied abruptly, as though he hadn’t been expecting to be asked. 

“How do you feel about that?”

“Not really a fan, actually. I mean, lions have a ton of sex, right? And those barbs on the cock? I didn’t really want to be female. A male might have been OK, I guess,” Jon remarked, having not been a cat yet, either.

“Well, you don’t have to have sex during the change, you know,” Matt reminded him. “It’s all consensual, right? The changes do put you into heat, though…”

“Yeah, I just hope I’m not into it. Fuck, that’s a scary thought!” Jon exclaimed, and both of them laughed. 

“Same, honestly,” Matt said, though Jon wasn’t sure if he was being serious or not. 

“Man, I’m surprised you’re going to be pregnant,” Jon brought it up again, still a little stunned. It had to be a daunting prospect, especially for someone becoming a rather larger animal. 

“Yeah, I mean, I’ve always wanted to be a horse, so I figured why not go all in?” Matt remarked, looking down at the vial. 

“Well, no time like the present,” Jon said, though it was impossible for him to project an air of confidence. Not that he figured he would be able to avoid a gender change as part of the program, but now that it was time, Jon worried that it would be a little too much for him to handle!

“I think Sarah is going to check on us soon, so we’d better,” Matt reminded him, uncorking the vial with the nanite solution that would change him. 

“Cheers!” He said, and Jon clicked the vials gently together before drinking them down. The fluid was bland and tasteless, as they had come to be familiar with. 

“How long is it supposed to take this time?” Jon asked, having forgotten what he’d read from the project sheet. 

“Umm, 4-5 hours, I think? Hands are the last thing to go. I think it’s so we can make notes and stuff during the changes as long as possible,” Matt replied, sitting down at his computer. 

Jon did the same, not really sure what to do with his afternoon. He wanted to try to write down what he might expect the changes to entail, but it was far too early to note anything substantial. So, he figured he would try to at least get a little bit of work done, trying to focus, though so anxious about the changes it was nearly impossible. Numerous questions rushed through his head, like what the genital changes would feel like, how those animals experienced orgasms, and what periods of heat or estrus were like. Hell, from Matt’s perspective, what would it be like to be pregnant? That, in Jon’s mind, was too much to think about!

“Hey man, I think it’s starting!” Matt exclaimed, and he moved from his laptop to show off his hand. The nails were starting to thicken, almost visibly as their skin shade began to darken. While it was happening to all his digits in tandem, both men knew that would not be the end goal, and he would only be left with one in the end. It was an interesting facet of the change and something he was sure to note in his report!

Figuring the same would be happening to him, Jon raised his own hand, the nails noticeably sharper. They, too, were thickening, likely to merge through the skin to form the base of retractable feline claws. Such observations were something he’d learned to make over his tenure in the course, and with the variety of forms and features he’d taken on, Jon never grew bored. The process was fascinating, changing every aspect of their anatomy while leaving their humanity and control intact. 

As was generally the case for full-bodied transformations, it was the soft tissues that started changing first. That came with a fair bit of itching, hairs within their follicles thickening and irritating the skin as new ones burst out around them. Such happened in short bursts, forming small patches in various places that made it hard to see the skin. It was enough to cause some annoying itching, and the pair decided it was best to take off their shirts. Still, it was hardly the first time they had been nude with each other, especially by the end of today, after all!

“Hey, I think my ears are starting to change,” Matt noted, reaching up to show them off. They were indeed enlarging, the skin heating up and molding into new shapes. Soon, they were noticeable under his hair, growing in real time. Their tips became pointed, and the canals swelled far larger than he was expecting. It was strange to see them settling on his head before his skull altered for a more natural equine visage, though such was common in the early stages of change.

The sight of it drew Jon’s hands upward, though he was already aware of the tingling that was a prelude to his own ears changing. The tips of Jon’s ears were not pointed, but rather rounded as they stretched out along the side of his head. It was a little silly as Jon looked into the mirror they had set up, and he couldn’t help but giggle. The changes sometimes took on rather amusing shapes as their anatomy altered from human to animal, and Jon took some selfies as his ears altered. Matt did the same, giggling as they had some fun. Jon even saw it fit to pretend to bite the soon-to-be horse, something that Matt protested, lest Jon wanted a hoof to the face!

“Man, I always miss this whenever I turn back,” Matt remarked, rubbing his ears. Jon didn’t need the context, knowing exactly what he meant as Jon’s own ears continued to curl slightly. His canals were widening as long hairs sprouted from within. Many mammalian species had superior hearing, and it was almost akin to turning down the volume on a laptop when it was time to change back. Jon’s ears twitched in reflex to sounds from outside, students and lawn care professionals, and other distant things that had escaped their notice. Nothing too interesting, though that would change when they moved to the barn area for the weekend post-change. There was a facility on site for people to spend time with animals, either students in their class or others paying for the privilege to become study aids. It was generally a buzz with activity, and Jon didn’t mind the idea of staying there for a few days unless that was he was unwittingly tempted by a lion!

For now, each man was delighted with their changing ears, rubbing them into being as the tingling increased in intensity. They were soon large in comparison to their human counterparts, and Matt delighted in twitching them once they gained the ability to do so. It was likely as much a consequence of needing to relieve the irritation of velvety fur they were to gain. The sight prompted Jon to rub his own, equally happy to feel the soft texture of short hair over their widening backs. It was softer than he expected, though he couldn’t have known what a lion’s fur felt like, so far removed from domestic cats!

The hair growth was not limited to their ears as Matt turned around, his already longish hair starting to take on a more straw-like quality. He shook his hair a little, some strands getting into his eyes as he commented, “Because I’m worth it!” Jon reached up to touch his own hair, though other than the short prickling up his neck, there was nothing of note. “Damn, I wish I was getting a mane, too,” Jon lamented, the implication of his wanting to be male not unnoticed. 

“Oh, you might have one on top of you by the time the weekend’s out if you know what I mean,” Matt remarked with a wink. Jon felt himself blush at that, not wanting to admit there was any chance he might like the new body and heat enough to mate.

With the transformation underway, both men settled back to their laptops, trying to get whatever work done they could before the more noticeable alterations. Itching played over their chests and bellies, thickening in patches to fur over their treasure trails and areas where hair already persisted. They stopped to scratch every now and then, though to be honest, there was little point until the fur took over entirely. Still, it made any homework impossible to focus on, and the two turned to gaming, stopping every once and a while to make some notes. The changes remained superficial for the next little while, with more fur and shifting human hair, longer nails, and thickening skin. Patches on Jon’s toes and fingers were starting to darken slightly, and the sharpened nails on his feet made wearing socks impossible. Matt struggled with his mane getting into his face, and his nose and lips started to thicken a little, peppered with minute hairs. Jon’s beard had altered toward the consistency of fur as well, though it had not quite spread beyond what his face normally sported.

“Hey, you hungry?” Matt asked, standing up. “I guess I have to go vegan for a while, you think? I can have sugar, though!” 

Jon nodded, getting up to join Matt in the kitchen. “Is it OK to eat during the change?” He asked, having not undergone one that took this long. Surely they would be fed in their animal forms, but he didn’t think he could last that long. 

“Should be. The nanites aren’t going to-oh wait, there’s Sarah!” Matt exclaimed, seeing their TA walking up to the residence. 

“Good timing. We don’t have much here. Unless you head out to graze,” Jon teased, and Matt had to giggle at that as well. They barely waited for the buzzer before letting Sarah in. “Everything going good?” She asked, pulling out a tablet to make some notes. 

“So far,” Matt said, finding an apple and taking a bite. Jon found little for his own appetite, though he figured Matt had much further to grow and would likely do better with something to eat.

“I’m just making the rounds before I get everything set up for the ‘extra credit students,” she commented. “Someone took the form of a lion as part of this module, so Jon, you’ll be taken care of if you want. I had to grab someone to be a stallion, Matt needed one with the right DNA for, well, you know,” Sarah added, blushing a little. Matt would have as well, though he seemed more excited about the process. Jon couldn’t help but blush as well, not sure how he would feel in the same circumstances. Then again, the fact that the option was there left him all the more nervous. 

“Sounds good! I’ll be waiting!” Matt exclaimed with more confidence than Jon figured he could ever muster. Sarah, to her credit, just smiled, heading out to make her rounds. Jon breathed a sigh of relief, not the first time he was seen in the middle of change, but never something he was fully able to get over. 

Matt, for his part, seemed to hold none of that same nervousness. He was eager to bite into his apple, reaching back to rub at the back of his pants, above his spine. Jon wasn’t expecting him to turn around, but as he did, the sight of a nub there gave him pause. It was rather sizable, and Jon was prompted to reach and feel his own backside, feeling something he wasn’t expecting. Damn, he hadn’t realized he had been starting to grow his tail!

With that, Matt felt it was time to strip down to his underwear and even take those off. Jon wasn’t inclined to look at his butt, but the nub growing from his spine was rather impressive. It slowly began twitching, not of its own accord but rather with the steady growth of its development. It was larger than he might have expected, though still the same pale shade, something he was quick to tell Matt. He’d never seen a bare horse’s tail before, and the sight of it was rather surprising, to say the least!

“Want me to look at yours?” Matt offered, and Jon hesitated only for a moment as he stripped off his underwear as well. He was sure his own lump was smaller, especially in comparison to Matt’s before he had a chance to expand to a mare’s proportions. But it was strange to touch, and eventually, they both made their way to the mirrors, turning around and looking at their soon-to-be butt appendages. It was fascinating to witness, especially as they slowly grew in real time. But as tempting as it was to stay and watch them, both agreed to sit down and work on their notes for their eventual essays, careful about their new growths as they did so.

The more his tail continued to extend, however, the more Jon felt a tingling in his loins, which was not uncommon from the change. A part of him wished he were able to put his pants back on to hide his erection. But there was little point given their oncoming changes, and besides, he didn’t need to look over at Matt to see his own cock was erect. It was obvious he was trying not to touch himself, leaving one hand on his tail and its slowly growing fur, with the other typing. But as a deep grunt escaped his lips, it was obvious he wasn’t intending to keep them stationary for long. Son, seeking fingers moved around his waist and groin as he shivered his lust.

For once, Jon had planned not to touch himself during this full-bodied change. After all, male genitalia were not part of the package, and there wouldn’t be anything to add to the report. But Matt had no such intentions, reaching to rub his own erection with intent. Jon would have felt embarrassed, but it was hardly the first time the pair of them had done such, even in front of each other or their classmates. The changes were really arousing, after all, and it was hard to really help it. As much as he wanted to hold off, the sight of Matt doing so was too much for him to resist. A brief shudder escaped his lips as he did so, the sensitivity more than he had expected. 

“Damn, took you long enough,” Matt teased, Jon blushing at that comment. 

“What, we don’t have to report on cumming from our cocks!” Jon countered, to which Matt simply giggled, 

“And what about clearing out the human seed before our junk changes? Not going to talk about that?” Matt retorted, and Jon had no real argument for that. 

Trying not to make a competition about things, Jon went to stroke his cock, rubbing his nipples in a bid for extra stimulation. Yet, he couldn’t help but look to see Matt teasing his tail stub in tandem with his cock, like the novelty of changes themselves was the best stimulation he could recieve. Jon couldn’t deny the temptation and eventually reached back to massage his own tail, the sensitivity more than he was expecting. Especially if he was able to reach behind the base of it, finding an unexpected sweet spot that left him shivering in anticipation. 

“Man, can you imagine having a cock the size of a horse’s right now? Not that I won’t be taking one soon enough!” Matt laughed something that left Jon a little abashed. He was expecting Matt to be willing to mate, given his agreement to become pregnant. But the fact that he was thinking about it already left Jon a little worried, blushing at the implication!

“What, I bet you can’t help but think about lion cocks right now, am I right?” Matt asked, making Jon blush even harder. He had considered the notion, though he had been hoping he wouldn’t have the choice laid out before him. But knowing someone was turning into a lion for the same span of time made him more than a little nervous. Especially given he might very well be in heat and begging for it by the time he was done!

As ashamed as he was by the idea, there was no denying how close they were getting, especially while rubbing the lengths of their tails. Matt’s horse appendage already had the start of wirey hair poking from it, and if he focused on it, he seemed to be able to swish it just a little. Jon couldn’t quite move his own; by the pricking of hair at the end of it was a sign it was developing properly. And the length of it was more than he was expecting, as the tip itched insistently. Any facet of the change, hot as hell as it was, drew them closer and closer to the release. As Matt moaned out, allowing his orgasm to happen, Jon felt his own end coming far too fast for him to even think about getting a tissue or anything of the like. 

The feeling of warm cum over his groin was somewhat pleasurable as his cock throbbed and unleashed its load. Jon didn’t particularly feel that his testicles were being emptied, but that was likely to come sooner or later as they changed. Matt, too, had blown a sizable load over his groin, rubbing the wiry hairs over his tail and jerking his cock all the while. The scent in the air was rather potent, and much to Jon’s surprise, perhaps a little stronger than he was expecting. It was nice, and he was left to enjoy the afterglow for a few moments, trying to think of how he would word it in the report. 

Going to clean up while he still could, Jon was a little surprised to notice his cock, even in its flaccid state, was a little shorter than he was used to. That was to be expected, as much as the changes were going to eventually make him female. He had to admit, the idea still made him a little afraid, though there was little he could do about it until the changes were over and the weekend passed. So he did his best to brace himself, heading back out to find Matt sitting down to type some notes. As much as he teased Matt for his overeagerness, it was nice having someone to not only normalize the changes but find some joy in them.

Before Jon could sit back down, a tingling in his chest caused him to reach up to rub at it. A gasp escaped his lips as his fingertips caressed his nipple, not something that was an erogenous zone usually. But in the midst of change, it seemed he was far more inclined to play with them, feeling his cock stir even he did so. It was powerfully erotic, too good for him to realize that Matt had turned to him, a wide grin on his face. “Nice to see you getting into it,” he teased before a confused expression crossed his features. It seemed his own nipples were in a state of change as he reached up to tease them, moaning out, “Oh, fuck…” as he did so. Jon had to look, Matt’s nipples looking even larger and darker than his own!

Jon couldn’t bring himself to focus much more as his own nipples beckoned him, and he rubbed at them, careful since he’d forgotten his somewhat sharpened nails. Their sensitivity went far beyond what he was expecting, and Jon could barely suppress a growl as both his hands played with their contours. If anything, in the ensuing minutes, it seemed they had grown smaller, though no less pleasurable to the touch. And as recently as he had just cum, Jon was a little surprised to feel his erection coming to bear, albeit smaller than he was used to. But he couldn’t bring himself to spare a hand to play with it. His nipples felt so damn good, and besides, Jon was sure he would be able to cum again from touching them alone!

Yet, he was a little surprised to feel a tingling further down his chest, around a patch that seemed to have more hair around it than he was expecting. Allowing a finger to dip lower, Jon was shocked to discover there was another sensitive nub there, almost as potent as the ones above. His other seeking hand teased the opposite side, where his fourth existed, and it was all Jon could do to contain his excitement. It was hard to believe his nipples were this pleasurable, though it was likely a facet of the change rather than anything lions felt in the wild. Still, he was there for it, wishing to rub them into existence. To his further delight, a third was formed below, and there was no denying Jon’s thoughts teasing the idea of maybe having them inflated a little, and nipped on by…

Jon’s self-pleasure was only stunted by the sight of Matt teasing his own twin pair to much greater effect. Even as Jon could feel his nipples migrating gently across his chest, Matt’s nipples had much further to travel. They were engorged as well, looking more akin to breasts as they descended toward his belly and even further. The skin was black and leathery, nipples thick as Matt groped them with both hands and let out excited gasps. It seemed, much to Matt’s delight, that they were growing toward a mare’s proportions before the rest of his body had expanded to catch up. And as they eventually settled just above his cock, it was obvious their size was barely an inconvenience. Matt was eager to drown in the pleasure, grunting and snorting in a way that was more equine than Jon had expected.

With his persistent groping, Jon was sure he was going to cum hands-free and didn’t see any reason for him to hold back. With a bit of a squelching sound, his testicles unloaded what was left of their burden, getting more cum all over his groin. The scent was rather sweet, and Jon moved to rub at it, finding that some of the hairs had changed a little in the last few moments. But what was really concerning was that his cock, even while deflating, was far smaller than what he’d expected, causing him to reach down with some urgency. Getting up, he was just in time to watch the nub of his penis pulled within his body, leaving only a small slit from his former urethra in an otherwise bare spot.

The sound of gasps from his roommate prompted Jon to look over to see Matt spasming with his own release. Much of his remnant sperm got on his leathery udder, and Matt was eager to rub it into the flesh, as though welcoming its growth. His cock, too, was steadily being absorbed into his crotch. Even as he reached to squeeze them one more time, his shriveling testicles were pulled within him, oozing the rest of his semen through his slit. What remained of his maleness was absorbed to be repurposed, and Jon was prompted to reach down to feel his own. The same was quick to happen and Jon could feel more cum leaking from his slit before the rest was completely ejaculated.

At this point, both men were left staring at their groins, waiting for the changes to their sex. It seemed Matt’s was to alter first, his genitals beginning to quiver as the remnant slit started to expand, running through the smooth flesh where his testicles once sat. As it did so, its contours pulled the skin within into a series of awkward folds of his forming vulva, leathery as the skin darkened to match his udders. It was growing larger, even through his perineum toward his anus. Strangest of all was that as its leathery contours properly blossomed, it started leaking its own stringy fluids, hardly the consistency of semen but potent smelling all the same. Matt wasted no time, rubbing his sex and moaning his pleasure. It was not the first time they had seen a mare’s sex, or that of many animals in the course of their program. But to have one in person…even Jon had to admit, the smell alone was doing it for him!

Naturally, it triggered a surge of wetness from Jon’s own sex, making him moan and reach down with curious fingers. The skin was perhaps even more sensitive than his cock head, and a part of him was left concerned. Still, it was likely a facet of the change, and Jon quickly allowed himself to enjoy it. His earlier trepidation had been swept by the wayside as he teased the new folds, cunt lips opening into a cavernous vagina, even though it was still small even by human standards. Seeking fingers sent shivers all the way through what was likely his cervix, though, in the heat of the moment, it was hard to focus on anything else!

As soft white fur continued to play over his groin, Jon let out a growl, one that sounded less human than he had expected. It triggered a similarly animalistic sound from Matt, and looking over, Jon was left staring at the massive leathery folds of Matt’s horse cunt. By now, it had migrated between his legs toward his rectum. It was the vaginal opening itself that kept Jon’s attention, nose flaring from the heady smell. Hell, Matt was able to make it twitch of his intention, looking almost like he was making it wink as he reveled in its development. 

“Damn…” Jon muttered, taking his hand from his own sex. It seemed a little too forward to play with himself when Matt was so engrossed with his equine sex. Matt took turns rubbing his open cunt as well as the bulbous udder underneath, the teats swollen and sensitive more so than he might have been expecting. Jon had a hard time denying that the same was the case for him, as much as his embarrassment had resurfaced. 

“Not going to join in? Want a helping hoof?” Matt asked, and Jon felt himself blush furiously. It wasn’t the first time such changes had led to sexual interactions when they were done, but…during?! 

Yet, the moment the offer was made, Jon felt his own loins twitching, contracting in a way he was hardly used to. A whimper escaped his lips, and without thinking, Jon simply said, “Yes”. With that, the man’s thick-nailed fingers moved to rub between his legs, tentatively seeking his moist, aching sex. Reflexively, Jon arched his hips, worried about the juices leaking over his friend and deterring his advances. Yet, it seemed Matt had no hesitation as he started to rub the outer lips of Jon’s new femininity, making him squirm from the contact. His new tail thrashed wildly, his clit far more sensitive than even some of the male forms he had taken on in his tenure as a student. And with that, it took him mere moments to reach orgasm, his entire body rocking from a very bizarre and foreign release. 

The scent of his new sex burned deep in his nostrils as Jon lay there, reveling in the orgasm and the touch of a good friend. “It’s not so bad to get frisky with your feminine sex, is it?” Matt teased, and as much as he had been nervous about it before, Jon couldn’t help but smile back. More than that, he wanted to share the fun around, and without a word, moved to tease Matt’s new horse cunt. It was a little intimidating, given the difference between Jon’s meager lioness sex and Matt’s impressive mare’s sex. And he certainly didn’t want to hurt his friend with his sharpened nails. But with as big and as sensitive as Matt’s new sex was, Jon was eager for the challenge!

Teasing the contours of Matt’s lips seemed to have little effect, given the sheer scope of what he was working with. There was some pleasure for him there, of course, Matt’s eyes rolling back as he took it in. But even with how close he had been, Jon’s meager efforts were not quite enough to bring him over the edge. Thinking of how Matt had just pleasured himself, Jon got the idea to start teasing his bloated nipples, causing a rather inhuman grunt to escape his lips. And with that, Jon worked both angles in tandem, getting up and giving Matt a grin before doing so with enthusiasm. His twin udders were enough to draw him close, and with some more confidence, Jon moved into Matt’s lips, rubbing their insides and making his larger body spasm. Finding the proper pace, he knew it wouldn’t take him long to achieve the desired result. And he was more than eager to allow Matt the same courtesy he had granted Jon. 

“Oh fuck…Ohhheeeeiiiggghhh!” Matt whinnied as he came, orgasm rocking his body and almost forcing Jon to pull back. It gave him a rather great deal of satisfaction, even as a strange fluid sensation covered the hand that was teasing Matt’s udder. His body was coated in a slick sheen of sweat, and Jon found himself lying back beside him, glad for the surprising moment of intimacy between friends. 

Coming down from such a release, it took both men a few moments to gather their bearings and get back to the assignment. Both reached for their phones, moving them down to take pictures of their female genitalia, even their swollen nipples. Matt had a hard time with his larger backside, having adjusted somewhat to allow his mare parts to fully form. He did his best to type while standing, though his stance was rather awkward. Jon couldn’t be sure, but it was likely their bones were beginning to shift under the skin. While the changes had largely been superficial thus far, the major muscle and bone alterations were soon to come!

With that came an acceleration of the persistent itching with their incoming fur growth. While there was an option to pick the fur coat and breed for their study species, little variety existed for Jon’s chosen animal. Matt had many options, though he settled on quarter horse with a mostly white coat. His fur was shorter, and as they watched, they could plainly see the skin turning black and leathery before the white fur took over. Jon’s skin was a different shade of pink than his humanity, though much of his belly and chest were covered, making it hard to see. It itched, though both were used to the sensations by this point. With the total body sensations they were experiencing, it would likely only be about half an hour until they were fully covered. 

As much as they wanted to make notes about their sex and the sensations of developing heat, the constant itching of fur made such rather tedious. It had quickly moved to cover their bellies and chests, outlining Jon’s nipples and tempting him to touch them as he scratched. He resisted the urge for now, making notes on his document about the contrasting sensations. Still, the ever-persistent prickling was annoying, especially as it played over his back and shoulders. Those spots were harder to reach, and he was somewhat tempted to ask Matt for help with those areas. But Matt was undergoing the same issues, trying to reach back and unable to scratch at the dirty white hair covering his back. It was getting harder for the two of them to simply sit there, scratching at the skin and moaning their annoyance. Besides, with the inconvenience of fully formed animal tails, it seemed more practical to move to the floor and forgo chairs entirely. 

No sooner did the two of them move their laptops to the floor than Sarah came back in, seeming to pick the most inconvenient times. Jon wanted to cover himself, though was at least thankfully able to flex his tail over his cunt, albeit just. Matt had more trouble with that, the long hairs on his tail itching the ones on his leg and causing it to raise reflexively. Worse, perhaps, was that the scent of their musty sex was palpable in the air, likely even noticeable to a human nose. Jon couldn’t help but blush, though Sarah managed to smile, professional even in such a compromising position. 

“The other stallion isn’t quite ready yet, but your body should need about half an hour to take to this,” Sarah said, and Matt moved forward eagerly to take the vial she handed him. Given the nature of this particular potion, she needed to wait until the mated male had his own DNA profile added to the mixture while in mid-change. But now that it was time, Matt drank it eagerly, even rubbing his udder and sex in anticipation. Sarah simply nodded, asking if they needed anything else before she returned with the changing stallion. This time, it was Matt who blushed, Jon able to smell the surge in his arousal. Matt seemed a little too into it, but at the end of the day, Jon was in no position to judge!

Over the next half hour or so, each man developed a thick coat of fur for their respective animals. Both were short, though thick enough that each couldn’t see the skin underneath. It had been weird feeling fur growing over their asses and backsides, itching as it fully covered their once-bare tails. Shaved beards erupted into their own fine coat to connect their neck fur and sideburns. Perhaps strangest of all was their human hair changing, though Jon hardly felt much difference when his already short-cropped hair converted to lion fur. Matt had a more drastic alteration to undergo, his hair getting longer and wirier, akin to the fur on his tail. He often stopped to rub it with his hands, but it was soon too unruly for him to deal with. “You should ask Sarah for a horse brush when she gets back!” Jon teased, though Matt moved into it, flicking his mane, though forced to constantly brush his mane out of his face. 

One somewhat surprising alteration was an eruption of thick hairs from around Jon’s nose, making him sneeze a few times to try and alleviate it. While knowing his whickers were coming at one point or another, it was still bizarre to feel them burst forward, tickling him as he moved to rub away the irritation. The level of sensitivity they possessed was rather impressive, and Jon lamented the fact that he had not tried possessing them as part of his program’s options for exploring animal senses. It was something that Matt seemed somewhat jealous of, rubbing his own bulbous nose and feeling much shorter, finer hairs covering its surface. It was still rather delightful to see them up close, and Jon timidly reached out to rub Matt’s face. Matt giggled at that, seeming to wicker a little from the touch. 

While the persistent itching of fur growth seemed to hide away any further changes, the tingling within their feet could not be suppressed for long. Jon was prompted to reach down, feeling the toes stiffening and the joints cracking and popping. He could almost perceive the tendons within breaking apart, and with that, he steadily lost the flexibility within. He could still manage to move them from the base somewhat, though they were obviously shrinking as he felt them. Reaching down to rub their bases, Jon was somewhat aware that the skin felt off to his touch, especially around his toe tips, and even below the balls of his foot. While the skin on his toe tips was rounded, the contours on his soles felt a little bizarre, and he didn’t need to turn them around to know it was becoming spade-shaped. Still, he was interested, never having possessed such paws and wanting to experience it fully. The difference in shade and consistency with the rest of his foot was fascinating, and only growing more so as the changes continued. 

Figuring Matt was undergoing a similar change, Jon turned to see his friend rubbing the base of his middle toes, which were decidedly thicker than the rest. It seemed his efforts were pulling out the center digit, drawing its length past the others even as they continued to shrink into the base of his foot. While each digit had started to form a thickening nail around them, the center nail had surrounded the entire toe. It was gradual, and Jon had to assume new layers were being formed within, living tissue to connect the toe tip with the developing hoof. A brief note of confusion crossed his features as Matt struggled to move his remaining toes. It seemed he had lost the ability, and it always was a little difficult to deal with such changes. But as his heels continued to lengthen, Matt seemed inclined to watch them go, wanting to see his middle digit grow the rest of the way and balance himself in a more equine fashion. 

“Feels weird. Neat, but weird,” Matt noted, raising the bottom of his developing hoof for their inspection. It was fascinating to watch the inner sections swell with spongy tissue as sturdy keratin surrounded it. The circumference of the middle toe was almost enough to match his heel now, though they weren’t much wider than his human equivalents, even as they changed. But the hooves at the end of them were relatively large, and Matt had some trouble lifting them, like a pair of heavy boots. 

A tense sensation in his toes stunned Jon for a moment as the nail bed sank into the tips. The joints and tendons needed to flex them were largely removed, save for at the base, which he could wiggle just slightly. One toe was entirely removed, but Jon was barely aware of it and had even missed it happening. The tension within his remaining toes was growing annoying, and he was thankful for the pain-numbing agent that prevented him from feeling the tips of sharp claws piercing the skin. Soon, the thick, sharp nails curved down toward the floor, and Jon felt with some delight that he could move them in and out, the tendons within having settled themselves. As bits of skin stretched out of his toe tips, Jon was left with the rather pleasant sensation of sliding claws through their feline fleshy sheaths, teasing them in and out in exploration. 

The sound of Matt clopping his hooves drew Jon’s attention to Matt’s delight, walking around and swishing his tail over his winking horse cunt. The heat was surely annoying, but he was loving the change, and even Jon was starting to get into it. His own massive paws were relatively heavy as well, and with his heels stretched as they were, standing was precarious. Not feeling the floor under his paws was strange as well, though it was fun to explore at the moment as they stumbled around while they still possessed the novelty. 

Figuring it was time to make some further notes, the sight of Matt’s head nearly hitting the ceiling gave him pause. It seemed his elongated heels, his thicker, muscled hips, and his expansive ass had added significantly to his height. Matt’s horse’s body was going to be a lot taller than Jon’s own, though it annoyed him that his equine ears had to be lowered to keep him comfortable. But as their lower legs continued to morph and alter, it was likely they wouldn’t be standing on two legs for much longer. 

An ache in his lower body was a sign of that, and Jon got down on his hands and knees, feeling his pelvic girdle popping apart and reorienting as his spine extended further. Now, in a proper position for it, Jon allowed his tail to swing back and forth in anticipation. This was generally the more jarring part of the change, the numbing agent not entirely able to stifle the discomfort. But as his hips realigned, more forward-facing as they swelled back toward his parting buttocks, the position soon felt more natural. It was a little uncomfortable to feel his anus pushed up against the base of his tail, and for his feline cunt to follow suit. But he had to admit there was something comfortable about his anus being devoid of fur, out in the open with his sex. And no denying it was in the perfect position to take a lion on his back, as much as he had been hesitant about such before. 

Matt was undergoing the same change, his backside further up in the air from his massive stature. His ass was massive, muscled, and covered with silky white fur to match the rest of his coat. With the lengthening of his legs and the barreling of his belly to support it, Matt was left with a rather comically sized horse’s ass before his front end swelled to match his equine proportions. Jon had to admit, the sight was rather funny, and he did his best not to giggle. 

“Man, this is not the most glamorous part about being a horse…” Matt moaned, feeling his belly continue to expand. Veins and stretch lines played over the skin before horse hair and hide came to cover it, leaving a rather uncomfortable strain on his face. It was likely leading to some uncomfortable internal changes, prompting Jon to remark, “At least it’s not as messy as being in the barn!” To which Matt gave him an incredulous look. 

The sound of the door opening caused both changing men to look up, hearing the sound of clopping hooves from out on the lawn. “Are the two of you able to move outside? I’ve got everything set up!” Sarah called out. While difficult, Matt managed to cartwheel himself outside, slow as it was. However, the moment the pungent smell awaiting him hit Matt’s changed nostrils, Matt felt himself shudder, horse vagina winking in anticipation. It didn’t take Jon detecting the same scent to know what was making Matt react like that. And there was a part of him who wanted to watch the show, as much as such would have conflicted him before. At the moment, he was happy for his friend, and almost wondered if he should have signed up for the same…

Outside was another man in the middle of change, though further along than Matt’s own. He still possessed hands, even as his chest barreled and his neck was left thicker than humanly possible. Like Matt, his backside was all stallion, with hind hooves, tail, ass, legs, horsehide, and belly of the beast he was becoming. Of most appeal, however, was the fully formed horse tackle underneath him. He was already semi-erect, either from the sex to come, his arousal from the change, or the mare’s scent Sarah had prepared for him. It mattered little as his thick horse cock slide from his sheath, dangling there below him and leaking from arousal. 

“He’s so big…” Matt moaned, and the stallion snorted, winking his way. It seemed he couldn’t talk well anymore, but it mattered little to either of them. The look in Matt’s eyes was one of hunger, and Jon couldn’t help but feel some arousal from the prospect as well. Not that he could ever take a horse, but part of him wished to ask for a lion. As much as he was embarrassed by the idea, he desperately wanted to get fucked, and the heat starting in his cunt was almost more than they could bear!

“Over here, Matt, the stand should be enough to support you both,” Sarah said, guiding him toward the stand she had set up. It was slanted to take his weight, with straps at the bottom for his hooves. It took some effort for him to make it over there, partially from his hybrid stance and partially from his arousal in the presence of the stallion, something he couldn’t avoid the gaze of. Tail raised and cunt winking, Jon felt a little embarrassed to see some piss leaking from Matt’s sex, though such was likely normal for horses. In the heat of the moment, Matt didn’t seem to mind, finishing before bracing himself against the stand and allowing Sarah to set him up. 

“You aren’t quite as changed yet, but from the size of your backside, you should be able to take it. You’re aroused enough, but I have some cream for you both,” Sarah explained, and Matt reflexively raised his tail, cunt winking and leaking. He didn’t bother to speak, feeling it was a little shameful to be a man in the moment of animal mating. Jon couldn’t blame him. It was important research in many ways, as much as it went beyond human notions of civility. But there was no reason why he couldn’t enjoy it from a human perspective as well as the animal needs that were part of the package!

Jon couldn’t help but watch as Sarah donned some gloves and rubbed the lubricant over Matt’s hindquarters, already dripping mare pheromones. Not that he needed the help, but it was to ease the process, after all. She then switched gloves to apply some lube to the horse’s cock as well, something that he stilled himself to allow to happen. The moment she was done, however, the soon-to-be stallion stomped his hooves, as though impatient for what was to come. And given Matt’s expression, he wanted it as much as his suitor!

Thankfully, the stand had plenty of room for the stallion to rest his weight as he reared up and started leaking over Matt’s backside, where he was able to land. He was inexperienced, and neither of them was fully changed, much to their frustration. Sarah was there to help, however, not bothered by the animal husbandry aspects as she moved to guide his cock in. Matt went to call out the moment his tight folds were penetrated, and the changing stallion was all animal as he pushed his way in, cementing their bond. 

For a moment, Jon felt some concern for his friend, thinking the horse’s cock might have been too big for him. Yet, all he could do was whine his pleasure, saying something akin to, “Oh yes…fuck me pleiiiggghhhsse…” which Jon had a harder time understanding. It didn’t matter, he figured, being obvious that Matt was into it. The other man couldn’t speak, but he was eager to push his way further in, almost to the hilt and beyond what Matt was designed to take. He let out a decided horse’s whinny as he started to thrust, and Matt’s smaller body was forced to rock against the stand as the stallion took his place on the stirrups and he bred for the first time in his new body.

Against his better inclinations, the sight made Jon reach down to rub his leaking lioness pussy, struggling to reach back where it sat under his anus. He was able to, if only just, though it was a far cry from the lion cock his new body required. There was no denying his regret for not asking for a lion mid-change. Even if it meant becoming pregnant, Jon wasn’t sure he was entirely put off by the idea. All he could do while watching the changing men going at it was wish there was a lion on campus that might give him the same experience. 

“It won’t take too long. Animal mating usually doesn’t. Just let it happen and enjoy it,” Sarah said, rubbing Matt’s mane a few moments before doing the same with the stallion. With that, the stallion thrust faster, and Matt was compelled to call out, “Give it to meeeeiiiggghhh!” his voice sounding more equine as he did so. Jon couldn’t be sure, but the spasming of his body was enough that he assumed Matt was experiencing his first true equine orgasm. Body frothy with sweat, he rocked there, cunt still filled with horse cock. His eyes fluttered in what had to be absolute bliss, and there was no denying Jon’s jealousy over the sight!

It seemed that Matt’s orgasm was enough to draw his suitor with him, rocking rapidly as he pumped his load within. He was noticeably larger as he fell off Matt’s back, cock leaking strings of cum as more dripped from Matt’s cunt. Neck thicker and rostrum enlarged, he reflexively pulled back his lips, taking in their combined odors once more. Matt was left stomping his back hooves, belly swollen toward equine proportions. The sight was more than enough to bring Jon as well. He’d been rubbing his own cunt lips all the while, and even though his touch was hardly a lion’s barbed penis, it was enough to do the job. As much as Jon didn’t want to bring attention to himself, he couldn’t quite stifle a growl, and Sarah did turn to catch him in the act. As embarrassing as that should have been, Sarah just gave him a knowing smile, and Jon smiled back, figuring she would understand from personal experience. And the more Jon thought about it, the was he was starting to accept the fact that being female was far better than he’d been thinking!

Heading back to her equine charges, Sarah moved to clean the cum leaking from Matt’s horse cunt as he stood there, swishing his tail. A look of absolute bliss was plastered on his human face, though it likely wouldn’t remain that way for much longer. His chest was starting to barrel, the bones and muscles within having expanded during sex to better take the stallion. It was mostly his face remaining, though a mane, equine nose, and flicking ears started looking more in place compared with the rest of his body. 

“You guys can head down whenever you want! It should be safe to change out here until you can walk, though. I’ve got a couple more errands to run, but I’ll be back!” Sarah informed them, and with that, the two of them were left there to undergo the rest of their changes. 

“How rwas it?” Jon asked as soon as she was gone. It didn’t escape his notice that his voice was a little gruff as well. He could always ask Matt once they had changed back. While he had been steadily changing while watching the display, it escaped his notice how his chest and neck had bulked up. He figured it was time for the final stretch, as it were. If he wanted, he could go back inside and manage to type a few things before the changes prevented it. Matt, with his current size, had no such ability, though he was hardly distressed about the arrangement. Rather, his tail was still swinging over his backside, looking like the happiest man in the world. Of course, he was hardly a human anymore, or even a man, but such was semantics with transformation technology. 

“Amazing, man,” he remarked, surprisingly articulate with the changes as far along as they were. Still, he twitched his mouth a little, finding it a little more flexible than he was expecting. As Jon watched, it seemed muscles were writhing under the flesh, veins fueling their growth as tendons popped and bones ground together. He was starting to grow his muzzle properly, a curious expression over his features as his gums expanded and his incisors started to swell, his face looking more horsey by the moment. 

Jon, too, felt the slight tension in his neck and cheeks, which was a sign his face would go the same way. The force made his whiskers twitch slightly and made him regret they hadn’t brought out their mirror. He was still able to work his way to the windows of the dorm, seeing his partially feline face reflected back at him. His jaw, too, was beginning to press out just slightly, lips parting further, and gums aching with the expansion of teeth from the roots. Grinning widely, Jon marveled at the sight of his canines getting larger, only as far as his parting gumline would allow for now. But as his dentures started to yellow slightly, Jon could only feel his excitement grow as the leonine changes took his reflection.

The slight expansion of his jaw forced his nose further toward blackened gums, and breathing in, Jon was further aware of his own scent. His feline odor was musky, potent with a spice that he could only chalk up to his arousal. Turning around, the scent of horses and sex became overwhelming, intriguing though far more pungent than he was expecting. The level of nuance from each horse was rather fascinating, levels of detail that made him breathe in heavily of their scent. More than that, Jon was aware that despite having just fucked, Matt’s heat was still present under their combined sex juices. 

It seemed that the temptation for self-pleasure was ever present, Matt straining to reach his nethers. Yet, as his shoulders rotated forward and he was forced to hold his hands out to stabilize, a hint of desperation crossed his larger features. “My udder is really full, man. Can you heeeighlp?” Matt asked, not able to reach back and rub what was irritating him. Jon was a little unsure what he was asking, though the sight of his swollen udder gave him pause. It was massive, looking out of proportion for his mare stature. Likely a facet of his unnatural pregnancy, as best Jon could tell, they must have been a full, if not painfully so. 

While a little nervous at first, Jon still walked over, sniffing the scent of his heat and feeling his own growing. It didn’t take much for him to get over his initial trepidation, especially since he had his hands to work over the flesh. A part of him wanted to taste it, reminded that mare’s milk was hardly worse for him than cows. That, and the fact that he was turning into a cat, worked well for both of them. However, it wouldn’t be long until his tongue charged, and keratin spines were likely not the most comfortable thing to use on Matt’s leathery sack. 

Jon was inclined to try his luck with his hands first, making Matt stamp his feet and whicker somewhat from the contact. It seemed as much a sexual thing as it was to relieve the pressure. Matt’s udders were easy enough to squeeze, though Jon had no actual idea how to milk a cow, let alone a mare. It seemed Matt was OK with his attempt, calling out with his desire for Jon to continue. Feeling encouraged, Jon worked his fingers over Matt’s udders, finding them damp as he started to coax the milk it. Curious, he reached to lick it from his hand, finding it a little pungent but not too offensive. It was enough that he was eager to keep rubbing, Matt excreting more milk and audibly calling out his relief. It certainly seemed to feel good, and even Jon’s slight efforts were enough to ease the pressure.

Yet, there was one more thing that piqued his curiosity. Jon did not think he could ever do so, but wanted to try it since the notion was firmly entrenched in his mind now. While his face was largely in a human state, he reached out with his lips to run them along Matt’s new teats. The texture was a little offputting, and efforts to suck provided little sustenance. However, using his hands in tandem was enough to have the proper effect, and soon Jon was able to squirt several gulps of milk down his gullet. The taste was a little too much, but the novelty was not lost. Jon kept it up, sure to have sufficiently helped his friend out with perhaps the most bizarre thing he would ever ask. 

“What does it taste like?” Matt managed to articulate, Jon looking up with a milk mustache of sorts. Without answering, both of them started to giggle, the absurdity of the situation not lost. He wasn’t being condescending, thankfully, not that he would be. Being in the middle of change really gave them confidence that most people never experienced! 

Eventually, the scent of Matt’s horse cunt grew too pungent for Jon to ignore. Not only was it arousing, but it awoke a curiosity that Jon couldn’t help but explore. Surely, Matt wouldn’t say no to a little teasing, being eaten out something the stallion hadn’t even gifted him. Matt’s mare ass was a little high for him, though Jon was able to get up on his altered haunches, sniffing the leaking fluids with some interest. While he couldn’t imagine such being that interesting to him, there was no denying the effect it had on his libido. Especially if Matt proved as into it as Jon felt!

With a curious tongue, Jon reached up toward Matt’s dripping horse cunt, teasing the edges. The sweaty skin was strong on his tongue, and there was a part of him that almost wanted to gag from his efforts. Yet, there was no stopping now, especially as a tingling against his tongue denoted its change. Expanding and flattening, Jon was given more space to work, his widening jaw making the action more comfortable for him. There was a chance if he was to keep it up long enough, he might even be able to make his friend cum!

“What are you…doeeeeiiiiggghhhh…fuck…” Matt called out as Jon went to work, teasing his leathery folds. While he was likely a far cry from what a horse would be able to do for Matt, it was at least able to make his massive body tremble somewhat. His twitching backside threatened to push Jon off him, though Jon was determined, balancing between maintaining his posture and ensuring Matt’s sexual pleasure. In truth, the sounds of his equine cries were enough to turn Jon on as well, and he was more than happy to put his mouth to the test. Jon would be remiss for not giving it a try, giving his friend a complimentary eating out as a reward for his female christening!

As Jon’s muzzle continued to extend just slightly, the added space allowed for a proper transition of his tongue. Its flattened shape made working over the mare’s winking clit all the more satisfying. And the pungent taste seemed to dull in his mouth enough that Jon could continue unabated. It was strange enough to feel the tingling over its wider surface as minute spines peppered it. As it changed, Jon resorted to using long, even strokes, making Matt call out with a rather equine cadence. It had to have hurt a little, but Matt’s mare cunt seemed made of sterner stuff, and he leaned back into it, evidently feeling an orgasm encroaching once more.

The sounds of Sarah’s footsteps approaching were almost enough for Jon to stop. While it should have been shameful to be caught in the act, so to speak, Jon couldn’t pull his feline tongue away. It was too exhilarating to tease his friend in such a way, and the idea that Matt’s mare tongue might return the favor was more than enough incentive. Besides, Sarah had surely seen worse acts for those transforming. “Oh, don’t stop on my account! You should enjoy it!” Sarah confirmed as she caught sight of their actions. Sparing her a glance, it was obvious she was grinning, standing and waiting until Jon had done the deed. 

It seemed she didn’t need to wait long as Matt’s mare cunt quivered from the attention. A long equine whinny echoed from his lips as Matt fell into orgasm, his massive horse body rocking from the intense tonguing. Jon had to wonder if he was the first horse ever eaten out by a big cat, but there was little time to reflect as Matt’s juices covered his nose. Eventually, Jon had to get down, the position awkward for his now-quadrupedal stance. Strings of fluids lingered from his actions, and Jon licked them with his larger tongue, not thinking anything about doing so. 

“Want the sameeeiiigggghhh?” Matt went to ask, though the equine inflections made such harder to understand. Jon didn’t respond, but rather turned around and hitched his tail up and to the side. His own lioness backside was quivering, lacking a male but turned on by the prospect all the same. It had been such a powerful turn-on to tease his friend, Matt’s mare juices still on his breath. And it was almost impossible to resist the urge to get off himself, growling his lust and finding little of his human voice present. 

Matt seemed eager to share the pleasure, able to easily reach down with his longer neck. Jon was larger than his human self, to be sure, but was thankful Matt’s head was changed enough for him to compensate for the disparity in their sizes. At first, his tongue and lips felt human, though in his lust, Jon didn’t really care what was teasing his cunt. Matt seemed to have some experience, having talked about ex-girlfriends in the past. Though Jon’s sex was hardly in the same configuration, Matt was easily able to get into it, even forcing Jon to adjust his stance in order to fight against the insistence. Matt was eager, it seemed, and somewhat ignorant of his equine strength. Jon was eager for it, however, already feeling the waves of pleasure teasing his body from Matt’s efforts. 

It was only to become better as Jon perceived the tongue teasing him growing larger. While it was too big to properly tongue a cat’s cunt, Matt’s changes gave him a bigger window to act, tongue teasing not only Jon’s lioness sex but his ass as well. It was almost too much to feel Matt slobbering over him, yet the tip of Matt’s tongue was doing amazing things to his insides. Eventually, Jon was able to take it to a degree, lowering his hindquarters even further as Matt’s changing muzzle worked to pleasure his feminine sex. 

Of course, the added stimulation was not for Jon to ignore his continued changes. He could feel the slight ache of bones altering, pulling at muscles, and causing them to stretch and tear to keep up. Jon was no more worse for wear as they rapidly regrew to reattach to his leonine bones’ new configuration. His growing muzzle seemed to slope somewhat, feeling heavy until his neck expanded to keep up. The size of it seemed to elevate his nose, and Jon breathed deeply, stunned by his olfactory abilities. Expanding nostrils allowed him to intake their feminine heat with far greater acuity, and Jon could only growl his contentment as Matt’s rubbery horse lips kept lapping at his cunt. 

As his face reached its animalistic contours, Jon’s new tongue explored the space within. In particular, he delighted in discovering that his expanding gum line had moved his teeth around before the dentation shifted to match a predatory diet. Grinding molars took their position in the back, and his signature canines extended down his blackened lips, sitting comfortably in a groove that had developed there. It was hard for him to keep his muzzle closed, however, as the constant tonguing to his cunt caused him to pant his lust. The realization sent a shiver of lust through his loins, giving him what was functionally a mini orgasm. Still, he was left only wanting more, and Jon backed up against Matt’s growing snout, indicating his desire. It was beyond his understanding to long for a lion’s reflection to stare back at him for the weekend. And as his skull compressed and his muzzle expanded, Jon was to be granted his wish!

What he had not been expecting was for the sockets of his eyes to suddenly expand, leaving them to water from the ache of it. Thankfully, Jon’s shifting skull was soon able to accommodate them as his eyeballs expanded and the irises surely darkened to amber. In the light of the afternoon, Jon was sure his pupils were forced into feline slits. With some relief, Jon blinked a few times, slow to realize colors had altered to his perception, green and red largely absent. He might not have noticed right away had he not recalled his research prep. And with how leonine his skull had become, Jon was sure his vision was set in stone, enjoying the enhanced acuity at a reasonable cost of a few colors. 

While he could barely do so against the persistent pleasure, Jon was still inclined to turn around and watch the same changes taking Matt’s face. His own had much longer to grow, obvious twitches of muscles and veins pulsating from his neck, and sending his face on its equine journey. Cheeks became massive as his muzzle extended, taking his incisors with them and leaving an intercostal space separating his grinding molars. Seeing his interest, Matt paused his oral ministrations to show off his thicker slab-like teeth, yellowing from the alterations to their enamel. Gums were thick and splotchy, and more flexibility was granted to Matt’s mare lips as he pulled them back in experimentation. Jon was aware from his studies that such an action was a response to a strong olfactory stimulus, and it seemed Matt was eager to experiment with his new ability!

Loud snorts and huffs escaped his equine lips as nostrils flared, taking their oval-shaped position at the front of his muzzle. Covered with short velvety fur, Matt reached down once more, teasing Jon’s backside before licking in earnest. Jon’s roar of pleasure was almost enough to take him away from Matt’s changes. By this point, Matt’s skull was largely equine, his ears moved to the top of his head, and his mane flipped over just above his massive eyes. His rectangular irises sat within massive equine eyes, pushed further apart as his muzzle took its proper shape. Jon would be sure to ask him what it was like to possess such a wide range of vision, though limited in acuity save for a spot directly in front of him. A fascinating contrast between predator and prey, one that they would likely eventually reverse with further full-bodied changes as part of their program!

Such thoughts were hardly a priority as Matt returned to teasing Jon’s cunt with vigor. Being so close already, Jon was unable to restrain a truly leonine roar as his own cunt went into release. The pleasure had been steadily building, likely prompting Jon’s new anatomy into a semblance of ovulation. That alone was enough to cause Jon’s entire backside to clench in orgasm. Whether lions in the wild experienced such regularly, Jon had no way of knowing. A horse’s tongue was able to reach in just far enough, thicker than a lion’s member, and far more dexterous. Matt’s rather pliable lips teased Jon’s his sex and even his asshole, bringing his pleasure far further than any natural lion. And Jon was left a dripping mess as Matt turned away, licking his lips from the feline fluids. 

“I brought these out for you, just in case. While it’s fresh in your minds!” Sara offered, leaving them a pair of notepads. While they were mostly changed by this point, their fingers were still functioning, and it made a lot of sense to get their thoughts down on paper. Still reeling from the orgasmic high, Jon figured his opinion might be somewhat biased, though it likely mattered little in the end. It was important for them to learn to feel the full impact of a female animal in heat. Such information would be vital for those taking roles as stand-ins for animal husbandry and breeding. And Jon couldn’t deny how valuable the first-hand experience was since he’d gotten into it!

Writing with their bodies in their current shape was troublesome, and Jon found himself wondering if he would even be able to read the mess when he’d changed. At least he could lower his head to see what he was writing, even if the color of the ink seemed washed out. Visual clarity was a bit better, at least, though, with leonine instincts, reading was rather boring. In truth, Jon had a lot to say and found himself making rapid point-form notes to expand upon when he returned to his humanity. At least he was able to make out the paper in front of him, something Matt was struggling with. His much larger body and head made looking directly at his paper impossible, and his notes were scribbled all over the place. He seemed frustrated, though it was likely all fresh in his mind as his final size seemed to settle in. 

Expediency was paramount as the changes made their way through their upper bodies, preventing their arms from moving in a way that let them write. Both their shoulder blades pushed forward, leaving noticeable bulges over their backs. With arms situated under their torsos, it was easier for them to hold their bodies up somewhat. The weight of their expanding torsos was a little much, especially for Matt, who ended up rearing over the breeding stand once more in support. Jon could manage somewhat, spreading his fingers to allow his arms to hold up his lioness muscle. The further his chest bulged out, the stronger he became, and there was a certain excitement for the jumping and running abilities his new form would cherish. Lungs took in more air, shoulders hunched down, and Jon found he could easily wriggle his backside in anticipation. Being a cat was more powerfully exhilarating than he had been expecting, and had Jon known it before, he would have eagerly embraced the form!

While Jon’s shoulders and upper arms were massive, they were nothing compared to the size of Matt’s own. His girthy flanks slowly expanded into his torso, ribs expanding, and chest barreling. He really was a magnificent specimen of a mare, as much as the serums were designed to make him into. It took him several tries to adjust his stance, whickering as his back hooves clopped against the ground. By the time the changes to his torso were done, Matt was only able to effectively move his arms below his elbows, compacted tightly under his chest. Not much use for writing notes, to be sure. But they were far superior for holding him up, allowing him to run, or perhaps more urgently, to take a stallion on his back!

With just their hands remaining human, the pair was eager to allow it to happen, wanting to enjoy their animal forms to the fullest. Jon felt his fingers reflexively clench as they started to retract, pulling inward toward his widening palms. It didn’t hurt, and as Jon relented from the discomfort, he found his fingers naturally thickened at the bases, moving inward as the joints popped apart and the cracking bones reformed into new shapes. A new joint formed within and pulled the base of his nail around a swelling of flesh from each digit, something he was now intimately familiar with. As his forming claws pushed their way out of the tips, Jon delighted in retracting them back within, then extending them all the way out once more. They were thick, massive, and even more impressive than the ones on his former feet. And this time he retained all of his digits, though his thumbs were pulled back against his wrists. Thankfully, he could still move them and delighted in doing so, feline paws more dexterous than he was expecting. 

As distracted as he was by his own changes, Jon spared a moment for Matt’s own, finding developing hooves just as interesting as his own paws. The swelling of his middle digits was familiar, if not still fascinating. Like Jon, Matt didn’t bother to wriggle them; rather excited to possess his front hooves and finish the changes. With his front side held up, he allowed the other fingers to pull into his wrists before losing their bone structure. His middle fingers swelled to take up the space, and Jon was sure he could tell where the particular bones and joints were expanding through the skin. Of most note was how thick his nails were becoming, starting to swell over the entire digit. 

Jon returned to watching his own hands finish changing, paws expanding rather rapidly to meet his new bodily dimensions. Palms continued to expand in proportion to his body, not as impressive as a male’s counterparts, but massive from what he was used to, all the same. Thickening pads carried that tradeoff from tactile sensation for stability, and Jon moved them across the ground a few times, loving the traction they provided him. Fur covered their backs and the spaces between his new feline pads, leaving Jon to revel in his lioness body, feeling his weight for the first time.

Matt, too, was experiencing the final changes, unable to hold his hoof hands up for them to see. Jon walked over and gazed up under the stand he was on, and was just in time to watch his inner hooves forming. It was rather interesting that an outer wall or shell-like structure covered an indent of softer tissue along the inside. If Matt was going to remain a horse in the long run, he might want shoes to protect the outer layer from wear and have them trimmed at regular intervals. Blood and veins ran through the inner area, making up spongy tissue that allowed them to take his massive weight even in the middle of a run. As best Jon could tell, Matt felt some pride in them, getting off the stand and clopping around a little as soon as he was able. Throwing his head back and hitching his tail, Matt waltzed around him, evidently loving the power and stamina his body possessed. Though Jon had it under good authority Matt was most proud of his mate cunt and what it could do for a needy stallion!

With their changes completed and their bodies functionally those of the animals they had been assigned, both felt a certain sense of displacement. After all, they were still outside their dorm, and while their program was well-known on campus, it was still a little uncomfortable to be an animal in such a place. Thankfully, Sarah had not gone too far and called out for the pair to follow her. Both knew the way, of course, but without hands, it was impossible to get themselves situated in their habitats. Even if most of the animals present were human themselves, it was still protocol to allow themselves to be guided into their enclosures, providing them with a more in-depth experience.

Of course, the two were required to give visual consent before entering their habitats if they wished to breed with anyone in male forms. Even being pregnant was not considered consent, though Jon figured Matt wanted more and was not surprised as he stamped his hoof yes. While it took Jon a moment to overcome his initial hesitation, Jon, too, nodded his head yes. Sarah simply smiled, seemingly figuring he would choose to. She even reached into her pocket, pulled out a tablet, and placed it on Jon’s tongue. “So you won’t get pregnant,” she explained with a bit of a chuckle. Jon was thankful, figuring that enjoying his female sex was one thing, but surely giving birth was more than he was ready for! 

As Jon walked into the literal lion’s den, the heady stench of male cat wafted over him, sending a shiver down his loins. It was impossible to fully wrap his head around the fact he was seeking out a lion in his habit, hoping to court him for a proper fucking. He would never have been so bold in his humanity, and part of him wondered how the male would feel about his presence. Who was this lion outside of this cage? Another student or teacher? After he changed back, would he run into whoever it was in the human world? Did it matter? 

There wouldn’t be long to reflect on such thoughts, as with a growl, the male made himself known. He was truly a magnificent specimen, Jon able to tell how healthy and virile he was by scent alone. It made his body weak as the male came to rub against him, Jon responding in kind. Reflexively, Jon’s lioness cunt opened and squirted a tiny bit of urine into the air, though rather than be ashamed, Jon could sniff the hormones that indicated his need to breed. The male was quick to pick up on this as well, moving behind him and audibly sniffing the air. Feeling his stance stiffening, Jon could only look back as the lion’s lips pulled back, something he recalled to be a fleshman’s response. Breathing in deep of his essence, the male’s penis sliding out of his sheath was a sign he was ready to do the deed!

Without really knowing why, Jon was eager to get down and raise his backside in the air, something he recalled as the lordosis position from his classes. He simply felt assured his hips were in the right position for the lion’s cock. It seemed the male was properly enticed, moving to lick Jon’s protruding cunt lips and eliciting a rather boisterous growl. Every cell in his body felt alight from the sensations. Jon wanted the encounter to continue more than anything he could recall. Being in heat, or a semblance of such, was the most intense drive he had known. Even if it was more a facet of the serums than a natural state of being for lions, Jon was there for it!

While the lion’s wide tongue was doing wonders to his cunt lips, Jon soon felt he needed more. Growling his irritation, Jon was thankful to have a mate who got the hint, so to speak. The weight of the male on top of him was more than he could bear, and Jon felt his body tense, wanting to take the great cat within him There was a part of him that wished he could talk to the male, wondering if he was a student or teacher or even a man in his human life. But it didn’t matter in the grand scheme of things, given the sheer ecstasy of the bestial sex he was about to experience. Especially the guilt-free fun their temporary forms granted them!

With his cunt on fire as it was, Jon was thankful for the sensation of the lion’s phallus pressing against it. His lips opened up like they were designed for it, and without hesitation, the lion pushed in, leaving Jon to grunt. As right as it felt, there was no denying the rather unique sensation of having a lion’s penis inside of him, stimulating his cunt lips and leaving him to shiver. Even if it wasn’t the thickest thing imaginable, Jon could perceive it working its way in before pulling back with a sharp pain. It took him a few moments to recall that a barbed phallus was rubbing against his insides, and Jon wasn’t sure he could take it. But as the lion worked its way over Jon’s back, there was no way he could get out until the big cat was done!

Yet, as the tawny beast thrust far faster than humanly possible, the persistent ache seemed to quell somewhat. It was as though Jon’s sex was being stimulated beyond the physical pain. His own orgasm was coming faster than he could imagine, far better than his previous masturbation or Matt’s equine lips. Likely, the spines were stimulating his sex into ovulation, and with it the gift of orgasm that kept cats going. With the force from the lion fucking him, Jon could only allow his eyes to roll back in his head and enjoy the release that his mate granted him. 

Almost shocked out of his reverie by a bite on his neck, Jon roared out before feeling the lion unleash his load. Jon could barely perceive it, though the sensation of spines leaving his cunt left him to roar once more. Part of him wanted to reach back and paw at the male, though he resisted the urge as he got up, looking at his mate. He was a little surprised when the male moved to sniff his cunt once more, and Jon relaxed into it, sex still lit aflame. He hadn’t realized it, but a minute amount of semen had leaked out of his cunt, and the lion’s tongue provided a welcome cleaning. Saving Jon the time of having to do it himself, he reasoned. And preparing him for the vaunted round two…

As much had Jon had tried not to think about it before the change, he was still rather aware of how often big cats fucked. With such little semen released from each load, lions and other big cats needed to mate dozens of times over a short period. Jon was well aware his heat had not abated and was eager to go again if the male allowed it. His tongue was rather pleasant, accentuating the afterglow and leaving Jon to shudder. But Jon was waiting for the main event as he got down and presented once more. Sticking his ass in the male’s face might have embarrassed him once, even less than a few hours ago. But as the male got on his back and started humping his cunt again, Jon found him wanting it more and more. He would eagerly present in any way a lioness might attract a lover, and as many times as the male wanted, he was eager to take his cum…

Matt, meanwhile, enjoyed the clop of his hooves against the ground as he was guided toward the barn area. Having become other animals in the past, he was familiar with the way there, though Sarah needed to go the same way regardless. The smell of horses, while normally strong, gave his altered mind some excitement, eager to be one of their number. There were only a couple in the stables at any time, all of them either students or graduates of the program. Some, like him, would be spending a weekend there, while others were there for longer. He heard rumors of people taking vacations as animals on the campus grounds, with the caveat of acting as a subject for the student’s lectures. In truth, Matt had no idea why these particular horses were here. So long as one of them was a stallion with a cock ready to go!

Knowing his wishes, Sarah guided him to a breeding stall, where a set of straps was set up for mares in heat. Even with his pregnant belly, the heat in his loins was persistent, and Matt saw it as a welcome experience to be bred as much as he was able. It would add to his eventual report on the experience, after all, and so long as there was a stallion willing to reciprocate, then there were no problems. As uncomfortable as it was to be strapped in the straps, Matt allowed it, knowing it would be worth it in the end. 

By this point, Matt was getting impatient, his horse’s cunt winking its deperatation. With his tail already raised, it was easy for Sarah to tie it back, allowing him to hold it steady without straining himself. All Matt could do was firm up his stance, waiting for the stallion to be brought in. He could smell him before he saw him, though, with his wider range of vision, the stallion soon loomed up, looking all the more masculine and powerful. Matt could feel his legs shaking, desiring to take the horse on his backside. Thankfully, the stallion was of one mind, reaching down with his broad nostrils and blowing hot breath over Matt’s nethers. With that, he raised his neck and whickered, lips pulled back in a fleshman’s response. It was clear the stallion was ready, and as much as Matt thought it might have been embarrassing, there was no denying he needed it in the worst way!

Without waiting, the stallion reared up, once more seeking Matt’s leaking horse cunt. With his body fully changed now, Matt felt it was easy to hold his weight, and enjoyed the fact that his body was able to take it. The stallion, excited as he was, took a painfully long time to hit the mark. Still, it had the advantage of rubbing against his swollen udder, giving Matt a brief shock of unfamiliar pleasure. A heavy whicker escaped his lips as the horse eventually hit home, and Matt felt his body being forced open, the stallion’s prick larger than he had been expecting. It was almost too much, making him grunt from the effort as he struggled with the weight of the beast on top of him. 

Yet, Matt was determined, thrusting back to try and take the beast further inside of him. It ached a little, the stallion using Matt’s body for his own pleasure. There was some satisfaction in that knowledge alone, being his purpose, and Matt welcoming his lot in life. Even though his body was technically already impregnated, it still delighted him to be fucked and mated. In the heat of the moment, Matt had a harder time distinguishing between his own pleasure and that of the mare’s instincts within him. It mattered little, in the end, he figured. Either way, it was his body and his pleasure to enjoy!

All the while, the stallion was thrusting faster within him, cock throbbing and stimulating his vaginal walls beyond his expectations. As much as the changing man had done it for him, there was no substitute for a full-blooded stallion, one with some experience to boot. It was obvious he had no intention of extending Matt’s pleasure, reaching down to nip the nape of his neck to hold him in place. In truth, the bestial insistence of the mating was what truly did it for him, and Matt allowed his growing orgasm to wash over him, nickering his lust. The powerful bite brought him over the edge, and in the heat of the moment, Matt could imagine nothing more erotic!

As strong as his vaginal walls spasmed from release, Matt was barely aware his male was also in the throes of orgasm. What felt like gallons of horse cum was pumped into his womb, both animals sweating and shaky from the exertion. Matt could only whicker as the stallion pulled out roughly, not caring to extend Matt’s pleasure as he panted his own release. Still, that was the way of things, and Matt felt he had little room to complain as he stood there, shaking from having taken the horse’s weight. 

While the other student moved to clean the stallion’s cock and sheath, Sarah was there to wipe Matt’s cunt of horse semen. Giving him a playful pat on the rump, she couldn’t help but comment, “Damn, you’re a natural at this! You should think about a career in animal conservation!” Matt hadn’t decided on what he was planning after his program, but if one of the prospects was charging into a female animal and being bred for reproduction, Matt could definitely think of worse!

With that, Matt was left alone with hay and the chance to relieve himself. It was late in the evening, though, as tired as he was, Matt found sleep evading him. For now, he couldn’t perceive any changes in his belly, though he knew the gestation was rapidly accelerated for the purposes of the program. It was a procedure they preferred not to enact in the wild, wanting the test species to have more time to bond with the surrogate mother. But in vitro, there were plenty of hands on deck to wean a new foal and hand it off to a reputable horse farm. The fact that his genetics would guarantee prized stock was a point of pride, and Matt found himself finally able to sleep, eager for what was to come. 

Yet, he could not have expected the weight in his belly as he got up the next morning, feeling off balance from the extra mass. His body was massively bloated and distended, almost discomforting, so Matt took stock of his new contours. Perhaps it would not have been so jarring had he been pregnant for the past ten or eleven months or so. But having the fetus nearly ready for birth already was harder than he was expecting, and Matt took a few tentative steps, doing his best to get used to his swaying belly.

To his surprise, Matt found his body wasn’t too inconvenienced by the added weight. Having not been around a pregnant person before, Matt was still sure it couldn’t normally be this easy. Not that he could go for a run or anything, as much as he felt his mare’s body could manage such the day before. It was a strange sensation, made worse by an uncomfortable pressure in his nethers. He was a little thankful when Sarah showed up, patting his rump before feeling his belly. “Feels good so far! I’ll have to run a few tests to make sure, but you’re shaping up well for a successful birth tomorrow. Good job, girl!” She teased, running her hands up Matt’s mane. And despite his sensibilities, Matt couldn’t help but take pride in the moniker or the task at hand…

******

It was sometime the next day when Jon woke from the familiar scent of his friend. Matt seemed to be exploring the grounds, the sound of his clopping hooves causing the well-bred lioness to look up. Jon wanted to greet him, though he figured there was little point. The sound of his lion’s roar might have been a little embarrassing if he startled Matt’s equine instincts. Instead, he kept watching his friend, the wind blowing in his direction and allowing him to detect the scent of sex. While his cunt was currently clean, he had obviously mated a few times the night before. Jon almost felt bad for him, unable to clean himself and likely needing some assistance before he could even have sex. Jon lost track of how many times he was fucked last night. And once the male woke up, Jon was all too ready to shove his cunt in his nose. Hopefully, that would lead to the rest of today being spent the same way!

Yet, it did not go unnoticed to Jon that the mating had another welcome effect. Matt was having some trouble walking, the size of his belly more than double what he’d seen on a horse before. It had to be uncomfortable, though Matt was able to trot around as though he had been born a horse. In fact, there seemed to be a glow of sorts in his eyes, as much as Jon could tell. He would ask when they were done, of course, but the expression on his face spoke volumes. Matt finally turned in his direction, sniffing the air and surely aware of what Jon had been up to. And rather than embarrassment over indulging with sex from a female perspective, Jon wore it with pride, actually willing to share his experience as much as Matt was once they had turned back…

******

It was some time the next week after the pair had returned to their human forms, working in the dorms on their essays. It was surprisingly easy, given the wealth of experience they’d had and their overall fascination with the changes. Jon, in particular, enjoyed his stint as a female cat and easily found it more enjoyable than some other experiences in the class. Certainly, it was far more visceral than he was used to from the program. Yet, after his successful trial run, Jon felt the confidence to try whatever else the program offered him. Especially if he could do something for extra credit, as Matt had.

“So, how was it? You know…” Jon finally asked his roommate, not sure how to word things, but shy the moment the words were out of his mouth. It went well beyond any standard conversation tactic he’d had, but given their shared experiences, was there really a less direct way to ask?

Much to Jon’s surprise, Matt simply blushed, only able to mutter that the experience was “OK”. That seemed odd, given his reaction to the change and his desire to be pregnant. There was clearly something else going on. Yet, as much as Jon wanted to question him, there was little he could do but wait for Matt to approach him and let Jon know what was on his mind. 

Oddly, Matt seemed eager to head back down to the stables that afternoon, asking Jon if he wanted to tag along. A little curious, Jon did so, even if Matt ended up evading the question each time Jon brought up the reason. A part of him already knew the answer, but he figured it best to wait things out and see for himself. 

To Jon’s surprise, their destination was not the stables on campus but rather a farm structure outside the grounds. It was a bit of a walk, though the closer they got, the more Jon felt things were beginning to make sense. After all, most of the ‘real’ animals they needed to keep on site were housed away from the student subjects. And what Matt was taking them to see would likely be out here.

Jon’s guess was confirmed the moment he laid eyes on the foal standing in the center of a paddock, frolicking around without a care in the world. She couldn’t have been more than a week old, and Jon was a little surprised she wasn’t growing faster, given her unnaturally rapid fetal development. Still, it seemed she would be given a natural horse’s experience, and even had a surrogate mare with an udder full of milk. Curious, the foal turned to look at the pair for a moment before turning her attention back to her mother. 

Not sure what to think, Jon turned his gaze to Matt, who was looking on with a seeming sense of longing. Jon was at a loss for words, wondering what it was like for him to…But soon, Matt turned back to him, grinning with pride rather than that look of longing or despair he had worn down here. “I bet she’ll be a champion someday,” Matt remarked, and Jon could only smile, figuring Matt would be spending more time volunteering at the stable for the rest of their program…