The African Queen (1951) - 3 major mistakes

Continuity: When Charlie Allnut grabs a bottle of gin from the box, all the bottles in it are wrapped with paper for transport. But when Rose Sayer takes the bottles out of the box to empty them into the river, the paper is gone (from the movements of her hand/wrist, you can tell that she doesn't unwrap the paper from the bottles).

Continuity: In the scene where there is a terrific storm while Bogart and Hepburn are asleep, Bogart gets extremely wet before being invited into the shelter by Hepburn. Upon entering the shelter and lying down to sleep, Bogart's blanket is perfectly dry.

Factual error: In the scene where the German East African troops are shooting at Bogart and Hepburn, their rifles are Gewehr 88 "Commission Rifles'" with five-shot magazines. In actuality, the German East African troops, under the command of Colonel Paul Von Letow-Vorbeck, were equipped with the absolute dregs of the Kaiser's arsenal: Gewehr 71 single-shot rifles, and Gewehr 71/84 8-round tube magazine rifles whose magazines usually got fouled and had to be used as single-shot rifles anyway.