refers to each of the thousands of hand-drawn sheets (of clear, transparent material, either celluloid or Mylar) representing a single animation frame to allow several layers of composition. Cels consist of character cels (containing only the foreground characters or objects - those things that move from frame to frame) and background cels, (static drawings of scenery that remain the same). The character cels are placed against the background cels and filmed or shot one frame (or picture) at a time to produce the effect of motion. Celluloid also refers to the thin strip of transparent plastic coating that forms the film's highly-flammable, light- sensitive base layer (such as nitrate base or acetate base); also used as an adjective related to some aspect of cinema (e.g., "the celluloid hero"); the light-sensitive substance coating on one side of the film base is termed emulsion; celluloid is also a slang word for a movie