Corrected entry: In the same scene where the blanket shrinks to the size of a cape, you can see Alvin's bed behind that has no blanket on it. You can also see Theodore's bed which never had the blanket taken off but that too is bare.
Alvin and the Chipmunks meet Frankenstein (1999)
1 corrected entry
Directed by: Kathi Castillo
Starring: Michael Bell, Janice Karman, Jim Meskimen, Ross Bagdasarian Jr.
Continuity mistake: At the beginning of the movie, When the monster loses his head, it is left next to him. But in the next shot, it's gone.
Mr. Yesman: So there you have it: I'm filled with terror and self-loathing, my job is hanging by a thread and I don't have anybody to entertain at tonights world premiere party. What do you think?
David Seville: Well, I can't help you with your bedwetting, but I can solve your entertainment problem.
Correction: Alvin's bed has no blanket on it because Simon is using it as a cape. You can only see the very top of Theodore's bed, where the pillow and the top of the blanket is. The blanket has a light green border at the top, before it is checkered. Which is what you see in the tiny bit of Theodore's bed that's in the shot.