Continuity mistake: When Droopy tells the bandit that he's going to serenade the girl in the photograph, he is holding his violin with its bow, but when the bandit picks up the donkey and winds up its ears, Droopy has the violin but the bow has disappeared.
Continuity mistake: When the bandit takes Droopy's wallet, he empties the contents and finds a photo of Droopy's girl. At this point, you can see the bandit is holding the photo with two hands, but when we see a close-up of the photo in the next shot, he is holding it with only his right hand.