When Puck meets Melissa she keeps him for a couple of days at her house, due to Puck's chaotic nature (and for strange reasons that are not worth detailing) he ends up inside Melissa's microwave, causing with his magical powers the microwave to get life, muscles... and the face of a cat for some reason, it doesn't make any kind of sense, but Melissa resigned herself and ends up being part of his life (how strange this woman's life is, jeez...).