I have a few cels and backgrounds that have the 
term "book" written on them and as far as I can 
tell they just seem to be part of multi cel set-
ups. They usually seem to be the layers of a 
scene that don't move in the cartoon or seem to 
be part of the background. In the case of my 
robot carnival book cel from Nightmare the 
traffic signals have book on them while the 
monsters just h