Revealing mistake: When the kids step out of the water and walk towards the house, the floor is already soaking wet from previous takes.
Revealing mistake: After Manco beats up Cavanaugh and places Cavanaugh's back up against the bar, while Manco faces him, three of Cavanaugh's henchmen appear at the entrance of the bar demanding that Cavanaugh be released. Manco turns around and kills all of them with his pistol, while Cavanaugh falls to the floor crawling toward his gun. Manco is walking toward the entrance of the saloon with his back to Cavanaugh. Manco draws his gun and kills Cavanaugh without looking at him. If you look closely at the tip end of the pistol, you can see that the only thing that Manco would have killed was the saloon floor. (00:17:00)
Revealing mistake: John Wayne suffers a broken arm and goes for a x-ray wearing a cast. At the bottom of the cast a slit is visible which allows the fake cast to be easily removed.
Revealing mistake: In the opening sequence when Colonel Ryan's plane has crashed and is on fire, you can see a metal pole supporting a burning aircraft shell, not a real plane.
Revealing mistake: In the scene where a tank is being pushed to the side by another, it's clear the tanks are miniatures.
Revealing mistake: At the very end, a violent storm engulfs Jerusalem and the people viewing the crucifixion. In the close ups, you can see rain falling, but no one appears to be getting wet.
Revealing mistake: In the scene where there is a air battle between a DC-3 transport, a American Corsair fighter and a Japanese Zero fighter we see some shots where model aircraft were used - it can be seen that there are wires holding the three aircraft up.
Revealing mistake: In the scene where the boy is shot in the leg and the carried away by an unionist soldier you can see more union soldiers storm past them. The bayonets of the soldiers are obviously made of rubber as they are dangling while the rifles are moved up and down by the running soldiers.
Revealing mistake: When Steve McQueen is in the hotel room very upset with Karl Malden because he was helping him win, he picks him up and slams him against the door. If you watch when this happens the entire wall shakes.
Revealing mistake: When Phil kills himself by throwing himself off the roof, in the shot of him supposedly hitting the ground it is painfully obvious that it is a dummy. Not only does it hit the ground completely rigidly but the wig on it even noticeably flies off on impact.