In Monsters, Inc., they appear at the beginning of the film, taking notes on how to be better scarers. They seem to be silent, even a little shy, while working. When Mr. Waternoose comes into the simulation room to moderate, he yells a tip at Bile, causing the pupils to jot it down in their notes.
Bill is a yellow, three-eyed monster with a horn on the top of his head and two eyebrows due to his Picasso-like face.
Jason is a green, four-armed monster with an eye on a stalk.
Trevor is a pink, four-armed, Frog, toad-like monster.