Continuity mistake: Caligula orders his chief gladiator to kill a prisoner so he can test the Robe's "powers". The gladiator stabs the prisoner with a dagger and straightens up. Look at the dagger and you'll see no blood on it.
Suggested correction: This may not be a mistake. It's entirely possible to stab either a person or an animal with a quick thrust and retrieve and show very little or no blood. Especially with a slim blade.
Continuity mistake: When Marilyn Monroe tries to untie the raft and Robert Mitchum can just catch the rope it the river flows from left to right. Later, when they take off again together, the river flows from right to left.
Continuity mistake: Shichiroji throws a spear out the door of Rikichi's hut in anger, it lands obviously in parallel with the door. Later, after Kikuchiyo's outburst he runs outside and picks the spear up, however it's now laying sideways compared to the door.
Continuity mistake: As the crippled airliner nears the coast, John Wayne slips his life jacket over his head, then provides one for another crew member. He then turns toward the cockpit, and his life jacket has magically threaded itself around his waist, and tied itself in place.