Suddenly Katies ass started to expand. "Are you OK?" Tiffany asked. "My butt!" screamed Katie suddenly. Her asscheeks bulged under her skirt und her panty started to burst. "Oh no! These fucking panty! It 's to close now!" she shouted. She ripped her slip hardly off und her butt expanded more. At last her ass had an enormous size. Proudly lifted Katie her skirt and showed her best friend her new huge ass. "Wow!" Tiffany shouted "When my best friend have such a huge butt, then I want to have it too." With a grazy grinning she took a swig and her ass expanded too. Her panty burst and soon she had also a huge butt like Katie. "Now we are two huge butt girls!" she shouted "Big butt girls, we are big butt girls! Eeeeeeeeeeeee!" Slowly the vial had an other effect on them. They started to get mad. And in their madness they did...