Rex is a turquoise worm with yellow eyes and wears a black collar. Rex makes few noises, but he pants and barks maybe once or twice.
Role in episode
In the episode "Dumped," Rex ironically, leaves on the bus after SpongeBob praises worms' loyalaty. Rex was only bought in an attempt to make Gary jealous and realize that he should go back to SpongeBob. The only trick he can do is "stay." He did not stay for long, considering the fact that almost immediately after that he went to the bus stop.