Dean continued to stroke the hard donkey cock, even as the boy's feet were hardening, his stomach and chest barreling out as his ass thickened.
Sam sat transfixed, his hand moving under his tented sheet to stroke his own hard member.
The boy's hands began to clump into a fist, hard dark nail spreading across it.
Dean moved sideways as he stroked, seeing the changes and him becomming top heavy.
"Mmmm mmmm, so gooood!" He bellowed as his face pushed into a full donkey muzzle, his voice turning to pure brays as he fell forward onto all fours.
Dean stopped stroking for a second to look over the full donkey standing there. The donkey was not happy at the sudden stop as he lowered his head, nipping Dean's arm, letting out a bray of displeasure.
Dean quickly started back up again, one hand playing with big smooth dark balls, the other stroking the huge member.
It did not take long for the donkey's brays to get more excited, soon shooting across the floor and Dean's hand. Dean moaned as his own shorts were now wet.
Sam grabbed some kleenex to clean up his own mess, shaking his head. "Woah, I can't believe you just did that... and I got off on it! What are we going to do with a horny donkey Dean?"
Dean just blushed as he felt his wet shorts, running to the bathroom.
Sam watched as the donkey dick slowly softened back into his sheath, a loud cracking coming from his legs, dropping him to his knees. His hooves were starting to split back into fingers and toes, stomach and chest shrinking as his face started to pull back in. A deep bray slowly turned into a human moan as his tail sucked in, his sheath disconnecting from his stomach, loosing its fur.
The boy slowly stood up as his fur thinned to thick body hair, his ears shrinking down.
Standing before Sam was an average 15 year old, aside from the slightly larger ears, hairy body and donkish penis hanging from his crotch.
"Fuck that was good!" The kid saying starting to pull his clothes back on.
"What was that?" Sam asked.
"Well I turn all the way into a donk when I get horned up, then change back once I cum. But I also slowly change over the course of a week if I don't get off. Guess I should be going, although kinda hard to warn others like this, tell your friend thanks for me!" He said walking out the door.
"Uh ok..." Sam said still hoping he was dreaming...