Book Worm is a highly intelligent worm who takes over the minds of any creature who consumes it. He is often used to help pass tests.
His only appearance was in Smarten Up!
Grim was going to give book worm to Billy to pass his math test, but Book Worm was swallowed by Milkshakes. Book Worm, while inside Milkshakes, attempted to tutor Billy, but eventually grew frustrated by Billy's stupidity. He later worked his way out of Milkshake's system, and was stuck in the litter box until Saliva swallowed him.
As his name implies, he is very bookish, and is even seen reading the encyclopedia for entertainment. He is highly intelligent, being an expert in multiple fields of study, focusing on math in the episode. He frequently uses large words, and speaks in a very formal tone, prefering to refer to Billy as "William" since William is Billy's full first name.
Although normally friendly and helpful, he grows frustrated by Billy's extreme stupidity, and becomes unwilling to help him, showing a low tolerance for Billy's stupidity.
He is a green worm with large glasses.
Milkshakes is Bookworm's accidental host, and thus Bookworm must try to make use of being inside Milkshakes' body
Book Worm attempts to tutor Billy, and at first the two get along, although ook Worm is rather annoyed by Billy. However, when Bookworm realizes that Billy is a complete idiot, he begins to resent and hate Billy. It also seems to annoy him that Billy thinks Bookworm is simply a smarter version of Milkshakes, and he shows annoyance when Billy tries to use cat treats to bribe him.
- He is a pun on the phrase "Book Worm" used to describe people who spend a lot of time reading and studying.