harmster
n. An evil little rodent that bites you every time you pick it up. Related to the hamster (in fact, indistinguishable from the hamster). It isn't until you attempt to befriend the thing that you realize the species difference.
Parent 1: Ben got what he thought was a hamster at the pet store last night. It bit him the minute he tried to pet it...
Parent 2: Must be a harmster.
Parent 2: Must be a harmster.