- Flint: "All right. Mr. Bile, is it?"
Bile: "My friends call me 'Phlegm'."
- —Flint and Thaddeus Bile
When first shown at the very beginning of the film, Thaddeus struggles with his test simulations, leaving a door open and utterly botching his attempt to frighten the mechanical child. He is accident-prone and a bit of a coward.
At the end of the film, he is seen returning to the Laugh Floor from a child's room, and he seems to have successfully made that child laugh, presumably by performing the accident he got in the simulation.
He also appears in Mike Wazowski's company play "Put That Thing Back Where It Came From or So Help Me", portraying the Sushi Chef during the restaurant scene, as well as singing with the rest of the cast at the play's finale.
During the event of Monsters at Work, he works as a Jokester and is shown to be able to spit out corrosive phlegm when he sneezes.