 Cels for _Dumbo (1941)_ (qv) are the rarest in the industry. The  animators, after the scene was safely "in the can", would strew the  used cels in the corridors and go sliding on them. In addition the  gray paint (used for so many of the elephant skins) would "pop" when  the cel was flexed. Many irreplaceable cels were destroyed this way.