Comparing the experiences so far, Mark realized the problem he'd had with being a jackass was that he'd been alone, and left his mental state human. All the awkwardness was from being a boy in a donkey body. And with no other animals around to associate with, he'd really missed all the possible fun.
"I want to try being an animal again, but this time, I want to be with a bunch of others like me. And I want to think and act like an animal, too."
Tony sighed and shook his head. "You don't know what might happen like that. What if you are in the forest as a deer? Thinking like an animal, you'll run away, and maybe get shot by hunters! Changing the way you think is really dangerous!"
"OK, so I'll pick something safe!" Mark thought a moment, and then grinned. "I got the perfect thing! When I was a jackass, there was a big field full of cows next to me. Cows stay in a field or a barn, they are always in a herd, and nobody would notice one extra."
"But then you'll get milked, and maybe screwed by a bull. What happens if you get pregnant?"
"The Chronivac should fix anything like that. Just program it so I come back just like I am now!"
Knowing he wouldn't talk the 13 year-old out of it, Tony and the others took Mark out to the same farm where he had been a jackass, and waited as the boy stripped and then stood naked in the field with the cows. "OK. Do it!"
Mark got larger and seemed to get older as he changed. His penis drew in while a bulge formed on his belly. Black and white hair spread over his skin, and he fell forward onto cloven hooves, fully a dairy cow. For a moment, he enjoyed the new sensations of being female and on all fours. But then he got confused.
Why was she here with the humans? Giving a low MOOOO, she turned and plodded back to her herd, memories of being a human boy mixed up with new memories of growing up as a heifer.
Tony and the others tried to follow the transformed boy, but she was lost among the hundred or so other animals that were nearly identical. In a week, Mark would revert to his human form,, and they would collect him then. They headed home to play with the Chronivac themselves.
Mark settled easily into her new bovine lifestyle, for she found everything quite natural. Sometimes, she would be aware of what she was, and that was always interesting - the first time she was milked was really strange. She didn't care much for the machine that tugged her udder until it was empty, but the feeling of a full udder was worse. On the second day, one of the humans noticed she didn't have an ear tag, and added one. It hurt when he first punched ear, but by the next day she had forgotten about it.
It was the fourth day, however, when Mark came awake to a new experience that he wasn't sure he wanted to try. One of the two bulls that wandered with the herd to keep the cows in milk snuffled her rump, and she felt herself responding like a normal cow.
Mark knew she could resist the urges and move away, but mating as a cow looked it might be fun. The bull was enormous, and she had come into season. The Chronivac would fix everything anyway, right? But what if something went wrong?