Well, Mary was a pig, a big fat pig with a cow's udder. While this was quite nice, being full and not caring about how you looked, Mary wanted to experience the full spectrum. Especially if that involved a means to get back at Rob for running out on her.
A vial caught Mary's attention. It was marked "Faerie". A faerie? Like Tinkerbell? Well now, that was interesting. Mary took out the vial in her fat piggish hands. Mary yearned for revenge on Rob and anyone who got in her way. Namely his wife, Amanda. What better way to exact her revenge than as a small faerie. She could creep around their house and not be detected. She could do anything to them she wanted. This was perfect! Mary giggled and squealed. She blushed, still a little unused to making animal sounds.
Mary uncorked the Faerie vial and downed the entire contents and waited for the changed.