Mary, annoyed at the lecherous pizza-delivery guy goes into the kitchen to get his drink. She looks over the vials and decides on the cow vial. Dumping the entire contents into an ice-filled glass with a can of soda, Mary smiles. She is dispensing justice to the world. There'll be one less man who can't think of anything but pleasuring themselves.
Taking the glass back out to John, Mary brings a can of soda for herself. She hands the spiked drink to John and sits across the table from him. She takes a slice of pizza and nibbles at it.
"Please, feel at home here." Mary says, waving a hand to the pizza and the drink. John, needing no second suggestion, drinks heavily and starts eating pizza. The pizza is spicy and John has to take many gulps of the spiked drink to quench his throat.
Mary watches John like a cat watching a mouse. She watches as the first transformation begins. John's nose has widened, the first stage to becoming a full bull. Slowly, his face protrudes into a half-muzzle and his tongue thickens and licks pizza sauce off his large nose.
John's entire body thickens with muscle. His neck swells out so that there is no change between jaw and shoulder. John finally notices his hand that has now morphed into an almost complete hoof. He looks up in shock and pushes back from the table. Staggering back from it and from the smug Mary he looks agast at his hand. He runs his hoof-hands over his body, feeling the changes that have taken place and parts of his body that are still changing.
A bulge in the back of his pants brings his hoof-hands around. They feel a long rope-like appendage lengthen and grow down one pant leg. A furry tuft tickles his ankle. "Wha...What going on?" John asks in panic. His voice has become guttural and he has some trouble talking as his jaw and face have changed.
Mary grins. "Oh, well, I've decided that the world would be better without you. Now really, I think you'll enjoy being a bull. No need for a job and you can have all the girls you want." Mary grins evilly as John is forced onto hands and knees as they change into cow legs.
John's body strains his clothing, massively muscled and a lot larger than before. They soon give way and show John in his almost complete bull form. Wiry fur sprouts all over his body, clothing him again. Finally, two horns poke up from his head.
Mary gets up to herd the newly transformed bull out the door. But, John panicked and bewildered shakes his thick head and snorts.