Ruben starting sniffing. "Whaaat is that smeeaaawl" he brayed.
Something smelled funny, it wasn't a smell Ruben has experienced before. His tail swinging behind him, Ruben walked closer towards the source of the smell, not paying attention to the hairs growing on his naked body.
He walked closer and closer to the jenny, as his penis started to erect. The jenny was in heat!
Overcome by his new beastial instincts Ruben approached the donkey, who turned around and presented itself to him.
Ruben stepped on a bench, and smelled... It was in heat, his penis was now leaking with precum, as his balls started to swell. Not being able to resist this new temptation, Ruben inserted himself in the female donkey and started to thrust, braying loudly.
The fur on his body had now completely covered him, his feet started to merge in to hooves as his legs and back started to turn into something more recognizable on a donkey then a human. However Ruben didn't care and kept thrusting his member into the jenny.
He approached his climax, and brayed victorious as he came and fell over backward on top of a bunch of hay, panting and braying.
"Did I just really do that?" Ruben asked to himself, now once again aware of what he did.
Ruben now also became aware of the recent changes. His body was now completely covered in donkey fur, his feet and hands turned into hooves and his arms had stretch into legs.
"This caaaaan't be haaaawwwpenning" he brayed, as his face started to push out into a muzzle.
Ruben looked down and then finally noticed that his penis had grown in length and had turned black with a couple of pink spots.
He rose to all fours as he couldn't stand normally anymore. "Heee haawww, HEEE HAAAWWW".
Ruben tried to speak, but could only bray. He was now completely a donkey.