In Pixar’s Monsters, Inc., Boo uses the nickname “Kitty” for James P. Sullivan.
Boo is a very young human child who enters Monstropolis after following Randall through a door. Because she has only a limited vocabulary, she gives Sulley a simple, affectionate name based on his furry appearance. “Kitty” becomes one of the film’s most recognizable recurring jokes and emotional details.
Sulley initially treats Boo as a dangerous contamination risk, reflecting the monsters’ widespread fear that human children are toxic. As he protects her, however, he becomes attached to her and begins acting like a guardian. The nickname emphasizes Boo’s innocent view of Sulley rather than the frightening image he presents to other monsters.
The name is sometimes incorrectly reported as “Sully,” which is the shortened form used by adult monsters for Sullivan. In the movie, Boo’s distinctive name for him is “Kitty.” Her use of the word also contrasts with the factory’s impersonal language about children as hazards or sources of energy.