"Well, I think I'll change into something else," Jess suggested. She was already feeling the novelty of being a pudgy pig-woman wearing off. Her clothes were uncomfortable, and she had this disturbing hungry feeling from the pit of her stomach growing stronger every second.
"Nonsense," Mary said, going through the vials. "You've gotta stay like that a while. You'll get used to it."
"I don't like this," Jess said. "I feel...weird. Wrong."
"Okay, look. I'll let you pick a vial for me to take, okay?"
Jess didn't want to play this game anymore. As her hunger grew, she began to concentrate harder on the thought of changing herself back to normal.
"Jess, pick a vial," Mary said with an impatient whine.
Jess oinked in frustration, surprising herself. Then she said "Okay, fine. Umm..." She looked through the vials as Mary held the box in her arms, but by now her hunger was too powerful to think about choosing from every animal in existence. "Umm...what were you before, a cow, right? Go back to that."
"All right," Mary said gleefully. Within a minute, she was changing. Jess was surprised to see that Mary was putting on a few more pounds, though not quite as much as herself. She watched a bulge under Mary's shirt grow and grow. As it poked out from underneath, she saw that it was a fully functional cow's udder, complete with four teats. Mary leaned back on her bed, enjoying the transformation. Soon her legs had been covered with fur, and her shoeless feet grew black hooves. A thin tail snaked around on the bed as it grew a large tuft of hair on its end.
Mary knew her changes were coming faster than before, but she didn't care why. She also could tell her transformation was going a little further this time because she had drank more of the vial. A headache alerted her to the new horns growing from her head. She could feel her ears stretch and stretch into cow's ears. She watched her fingers melt together to become much like Jess', except hers were being covered by short white fur. The fur was growing all over her body, with large black spots here and there. Two black spots encircled her eyes. Her breasts shrank and shrank until there was nothing on her chest but fur, meanwhile her udder filled out even more.
When the changes were over, Mary mooed in delight. Jess chuckled at the sound. Then her eyes darted to her brand new udder. The empty feeling in her gut began shouting again, but this time it wasn't just to remind her that she was becoming ravenous. It was telling her now was the time to feed.