"You want to... fuck a mare?!" Matt repeated, disgusted with what just came out of Tom's mouth, and also by the lewd scene in front of him. With Tom's massive stallion cock erect and sticking straight out of his body, it was hard to ignore. The large balls that hung in Tom's scrotum were also easily visible.
"I-I didn't mean to say that, I swear!" Tom exclaimed, hoping that by denying it, the changes would stop. Of course, the changes would not stop, and Tom's pants ripped clean off, revealing a hairy tail that happened to sprout right above Tom's ass. "It's just that... mares are... s-so... sexy and... they make me feel so... so good! Ugh!" Tom bit his tongue, trying to bring himself back to focus. Focus on being human and staying human. The animal serum inside him, however, had other ideas.
A growling, gurgling sound could be heard, echoing in the small room. Tom's stomach, normally flat, was starting to swell up, and out, turning into a stallion gut. Matt rubbed his hands all over Tom, feeling the brown fur that was steadily growing all over the half-horse, half-human roommate of his.
"T-touch my dick, please!" Tom pleaded with Matt, his hands already stroking the thick, leathery cock that stuck up in his face. "Rub it! It feels... so good!" And before Matt could even answer, Tom took the head of his horse cock into his mouth and began sucking, reveling in pleasure.
"This is insane... but okay..." Matt mumbled, running two fingers along the length of Tom's horse dick, with another hand holding Tom's heavy balls. They were slick with horse pre, and Matt could help but admit that the smell of horse fluids was starting to turn him on a little. ...Maybe not a little, but a lot.
If anyone were to walk in, they'd see a creature with the top of a human, but the bottom, a very very large bottom at that, of a stallion. The human's mouth was sucking on his own horse cock, and the other person in the room, a complete human, was blushing madly while he fondled his horseman friend's penis.
"God... this is so hot..." Matt said to himself quietly.