Corrected entry: In the scene where the snowman is falling in his globe and notices the emergency exit, if you look in the background, he falls past the same bookcase seven times.
Continuity mistake: The snowman hits his nose with a hammer, completely bending it in half. In the next shot it is suddenly magically straight again.
Correction: This is a nod to animated series like The Flintstones and the Jetsons, with their endlessly repeated backgrounds. It's satire, not a mistake.