Book Cels

 
 A cel with the words book on the top means that 
there is a foreground that is supposed to go in 
front of the cel. This foreground is usually made 
of the same paper as the background, but is cut 
to the exact shape of the item that is to be 
placed in this foreground.  

 Information curtosity of: Animation Production 
Information (www.kimonocels.com)