Mary picked a vial at random out of the box. It had a picture of a butt and mouth on it expelling gas.
"Like this will really work." Mary said, drinking the entire vial in one gulp. Then she waited for any effects. Nothing happened.
"I knew it-BURRRPPP!!!" Mary went wide eyed when she released a massive belch. Then her ass clenched up and she farted very noisily. The smell stayed in the room. She nearly choked on her own fumes. She ran back to the vials and quickly looked for a human vial.
"I've got to, PFFTT! BURRPPP!, change back!" Mary said, taking a swig of the first vial she got out. Unfortunately for her it was the pig vial. Mary looked on in horror as her ass started to gain weight. Then she burped and farted some more. Each emission causing her to gain more and more.