Christine grinned as she approached the tied-up stablehand. "Let's see how you like the sexless life of a gelding." She ran the brush across the boy's crotch, and watched his already-impressive manhood swellinto the sheathed equipment of a stallion - except that the area behind the sheath was smooth.
"No! Please! I don;t wanna be an animal! Especially not a gelding!" The kid struggled to get free as she used the brush on his belly, and then down each leg.
Mike looked at him in disgust. "You didn't mind doing it to me, did you? Well, now you get the full treatment!"
By now, the kid had the hindquarters of an Arabian gelding, and the enlarged body of a human teenager - but his chest and arms were altering fast. In minutes, the boy's size and weight broke the ropes binding him, and he fell forward onto fully-formed forelegs.
He had his homely human head and face at the end of a horse's neck, and a full equine body. Another touch of the brush enlarged his head to match, and his ears moved to the top of his head.
Christine stepped back. "You know, he's pretty interesting like this. A horse that can talk and think. Tell me, boy. Would you serve me as a mount until I am through with this adventure? I'll make you normal again when I get ready to leave. Sound like a deal? Or would you rather complete the change to animal?