All right then, this takes place season 6:
Plot A: Stephanie and Michelle are coincidentally assigned to bring their class pets home for the same weekend, and the pets do not get along. Stephanie's class pet is of course Fluffner the rabbit, I think it might work well for Michelle's to be a hamster.
Plot B: Meanwhile, Nicky and Alex decide they want a pet, and try to convince Jesse and Becky to let them have one.