Revealing mistake: When the elephants are making fun of Dumbo in the train caboose, Dumbo's mother pulls a pin which causes the stall door above the other elephants to fall. When the door bounces back up, you can see that the animators forgot to draw the elephants' heads and trunks and only their bodies are visible.GalahadFairlight
Revealing mistake: In the final scene where Miss O'Shaughnessy is in the elevator with the detective, the door closes and the elevator starts to 'descend', indicated by dark glass going down, supposedly because the lighted elevator is passing beyond the view of the exterior door. But if you look, you can still see the silhouette of Miss O'Shaughnessy behind the glass, not moving. It is just a piece of wood or something being lowered behind the glass to simulate the elevator going down.
Revealing mistake: A scene in which a group of soldiers appears to be running uphill was obviously filmed with a tilted camera because all the trees in the background are leaning at a 65-degree angle.