Revealing mistake: The professor has a blowout, but all four tires on the car are fine. (02:04:30)
Revealing mistake: When Atticus kills the mad dog, you can see its hind legs being pulled by someone off screen. (00:43:05)
Revealing mistake: There is a short section where a U.S. soldier hops a rugged looking stone wall in France. As he goes over the wall, it moves back and forth a bit as if made of styrofoam and wood.
Revealing mistake: Near the beginning, after the corporal has burned his finger and tells the other corporal that Lawrence is balmy, O'Toole begins to run up the stairs to meet with a general. After O'Toole is out of view of the camera, you can tell he has stopped running up the stairs by his shadow on the wall not moving, because he knows that the director is about to shout "cut".
Revealing mistake: When Ransom and Hallie Stoddard are riding the train back to Washington at the end of the film, pay attention to the view out the window as Hallie responds to Ransom's suggestion of returning to Shinbone. When the conductor brings the spittoon and talks to them, the same exterior footage repeats from when Hallie started to speak. (02:01:30 - 02:02:15)