Least weasel (Mustela nivalis sp.)

In spite of the smaller subspecies clocking in at less than half a pound (for comparison, domestic ferrets typically weigh at least a pound and a half), these little bastards are still quite capable of taking down a five-pound rabbit.  Babies are killing things by the time they’re two months old, which is rather to be expected from kits reared in dens lined with the skin of their mothers’ victims, so, you know.  Weasels.