It had been a full minute since Jennifer had inadvertently said the words "Transform or Dare" to Kelly, and since Kelly hadn't made a choice, Jennifer felt compelled to give her both barrels of the curse that had come to mind.
"You will transform into a person who's part human and part cow," Jennifer said, "complete with hooves, horns, a tail, and a nice big udder. And I dare you to, whenever anyone asks, let them drink some of your sweet, sweet milk."
"Oh, you have got to be kidding," Kelly said, but then she put her hands to her stomach and said, "Oh, my God." It was as if her belly was swelling with pregnancy, but no; her shirt was shrinking, revealing that the roundish blob that was growing there had four protuberances emerging from it.
Kelly was focused on the udder and barely noticed the rest of the changes to her body. Her nose flattened out and her ears extended outward as a pair of curved horns poked up a few inches through her blonde hair. A thick coat of short fur poked out through her skin, white with black splotches. A tail stretched out past the top of the waistband of her skirt, a blonde tuft on the end matching the hair on her head. She kept her human breasts, but because her now-smaller shirt now resembled a tent, it was obvious that those nipples had lengthened to match her udder.
Her shoes and socks disappeared to reveal that she now had hooves instead of feet. In fact, the entire bottom half of her legs had become decidedly bovine-looking. Her hands were more human-looking, although she now only had two hoof-like fingers and a hoof-like thumb on each. And she was using those to give one of the nipples on her udder an experimental squeeze.
As a little jet of milk shot out, Kelly froze -- except for the tail twitching slowly behind her -- as if she'd suddenly become aware of her classmates standing around watching all this. Then it seemed as if she'd become fully aware of the fact that she'd changed exactly as Jennifer had said she would. She looked down at the hoof-hands at the end of her furry arms, at her long nipples, at her bulging udder, and made a noise that came out as a half-scream, half-mooooooooo.
She took off running down the hall. Within 15 feet, she went sprawling onto the floor, not used to running on hooves and with an additional weight dangling from her front side. She managed to quickly get back up to a standing position and took off running again, this time more careful, eventually ducking into a doorway about two-thirds of the way to the end of the hall.
No one followed Kelly. They were still standing around, some open-mouthed, all staring at Jennifer.
Finally, one of the boys found his words, and said what everyone else was thinking. "H-h-holy shit -- the Goth chick has actual magic powers!"
This set off a panic as several dozen high schoolers went in all directions, all trying to avoid being cursed the way Kelly had been. Jennifer tried to plead her case, that she had been compelled to do that to Kelly and that she couldn't curse anyone else now that she'd passed the "Transform or Dare" power on to Kelly anyway -- but no one could hear her above the screaming and the stomping footsteps anyway.