When Chalice is showing Cuphead and Mugman her scare abilities as a ghost she makes snake like creatures come out of her head. This is a reference to Beetlejuice (1988) where the titular character scares the same way to the protagonists when asked if he can scare people.
The first victim of Chalice, Cuphead and Mugman in the theater is Sally Stageplay, one of the bosses from the video game.