Character mistake: The scene in the outdoor Parisian cafe is incredibly daft. First, the cafe owners call James Coburn's bizarrely-accented Australian to the telephone to keep him out of the way as their accomplices assassinate three uniformed German officers seated in the cafe in a drive by shooting. They then toast the killings with cognac, and that is the mistake - not the shootings, not the luring away of Coburn - the mistake is that the cafe proprietors celebrate the assassination of the German officers in broad daylight, in the open, without even stopping to think that such an action would have them shot, because all of this is done in the direct view of passers-by in broad daylight. Do they think those three German officers were the only ones in Paris? How did they know Coburn wasn't an undercover Gestapo agent or a French collaborator? Don't they stop to consider that in an occupied city machine gun fire is going to draw some attention from the authorities, who might just wonder what a couple of bullet riddled corpses are doing lying about the place?
Character mistake: When Werner goes to see Hedley for helping finding his "lost" papers, Hedley is playing chess. The chess set is set up incorrectly. When the men are set up properly, each player has a light colored square in the right-hand corner. In the movie, the game is set up so that the light-colored square is in each player's left-hand corner. This "beginner" mistake puts the king and queen in the wrong positions.
Character mistake: When Werner asks Hendley why, as an American, he fights alongside Britain, he mentions that the British burned down the U.S. capital in 1812. While it happened during the War of 1812, the burning of Washington actually occurred in 1814.