Revealing mistake: In the scene where the Bear Jew beats the German Sergeant to death with a baseball bat, the sergeant's head basically explodes into a mass of blood at the end of the beating. In a later shot, the sergeant's body is shown lying on the ground with the head intact. (00:33:10)
Revealing mistake: Hugo Stiglitz's eyes twitch when Hans Landa is inspecting his dead body.
Revealing mistake: When Bridget von Hammersmark is being strangled you can see a crack in the plaster on her leg, allowing her to take it off. Best seen in the shot taken from under her feet, right before she stops struggling.
Chosen answer: It is explained shortly afterwards that a real German would hold up his thumb, index and middle fingers to indicate three. Since, the major already suspects the Captain of being a spy, holding up his index, middle and ring fingers to indicate three confirms this.
Xofer