The Nuzzlet is about the size of a gerbil or a hamster. Other than its physical appearance, very little is known about it (other than the fact that it should never be fed any candy).
When Kick feeds it a piece of candy, he finds out too late that he shouldn't have done so. When he goes to retrieve it, he discovers it has turned feral. Its teeth and claws have sharpened and its eyes have turned red. From there, things only get worse when the Nuzzlet starts causing mischief. It bites when Kick gets his finger near it. It can now lift and move objects many times its size, and easily tosses Kick around like a rag doll. After an array of making trouble for Kick, the Nuzzlet gobbles down an entire jarful of candy. With a full belly, it suddenly becomes unstable and explodes, devastating the library.
After it lets out a belch, the Nuzzlet is back to normal. Kick stealthily retrieves the Nuzzlet and sneaks back to class. He tells about how violent and destructive it was and that no one had ever survived researching it. Ms. Fitzpatrick, unaware of its effects, gives the Nuzzlet more candy, causing it to blow the roof off the school.