Revealing mistake: When the Russians are in the Finn's trench, you see the Finns stabbing the Russians. If you look carefully, on a few of the Russians you can see protection visible. (00:48:45)
Revealing mistake: When the mice are feeding the cat, the cat sits up and a mouse passes through his head.
Revealing mistake: When Alvin and his mule get struck by lightning, if you look closely you can see the hair flip up on the mule's flank as he's hit with a whip to make him get up, and you can see the whip drag off to the side of the screen.
Revealing mistake: The French tanks that attack Paul et al. Towards the end of the second act are supposed to be Saint Chamond tanks. There is only one of those left in the world, and it is not on screen: the undercarriage and tracks don't even come close to looking like that of a Saint Chamond, because it's actually a BMP-1 dressed up to look like a Saint Chamond.
Revealing mistake: Whenever James, Sanborn, and Eldridge are riding in the Humvee, you can see panels of wood in between the doors and windows of the Humvee. If you look closely, the grain in the wood is visible.
Revealing mistake: When Buck and the gang ride away from the saloon in Dallas where JC made a few new 'friends', the footage is sped-up for a second just as soon as James Caan jumps on his horse. (00:05:50)
Revealing mistake: In one of the opening scenes the platoon of the captain is gunned down by a MG42. You can see the crimped fronts of the blanks in the belt.
Revealing mistake: As Uchida makes his last-stand the ships tilts heavily to the right, however none of the empty shells on the deck move, showing that it's only the camera being angled.
Revealing mistake: When Barry stands at his uncle's dinner table to supposedly "toast" Captain John Quinn for his pending marriage, to Barry's cousin Nora Brady (who Barry is in love with), he throws his glass in Captain Quinn's face instead. However, the glass noticeably breaks before Barry even throws it.
Revealing mistake: During the battle of the Chosin Reservoir, just before VF-32 comes in to provide air support, the Marines are firing their M1 Rifles. One of them mimics the recoil of it but we don't see the bolt move back when he fires his rifle. The M1 Rifle or Garand is semiautomatic, and the bolt moves back each time the shooter pulls the trigger.
Revealing mistake: When they are feeding Annie the Elephant medicine with a wooden spoon, there is obviously no fluid in the spoon.
Revealing mistake: At the start of the film, Sergeant Gunn and another member of his tank crew take shelter in a shell hole as they are returning with fuel and spare parts. Watch the supposedly dead soldier hanging over the edge as they leap into it - he visibly reacts and moves his head.
Revealing mistake: When Col. Franz von Waldheim first encounters Mademoiselle Villard at the museum and walks away from her to turn on all the lights, the wall to the right bounces like canvas as he operates the switch.
Revealing mistake: When there's a cave-in in the tunnel the POWs are building, you can hear, as the POW is tunnelling out of the cave-in, his trowel hitting the glass that separates him from the camera and crew.
Revealing mistake: A blank firing adaptor (BFA) is visible on the muzzle as the men set up the .30 caliber machinegun.
Revealing mistake: During the long tracking shot at Dunkirk, steadicam operator Peter Robertson had a little assistance in getting around. This took the form of a kind of golf cart (from the beginning to just after shooting the horses), and later a rickshaw (from little after the choir to just before the steps ascending the billets). If you look at the ground to the left just as the camera begins backing away from the carousel, you can see tracks in the sand made by the rickshaw. Keep watching the sand near the actors' feet to see more.
Revealing mistake: After Clint has shot the 3 would-be rapists, he is rifling through the pockets of the dead men. As he checks the pockets of the first guy he shot the "dead" guy in the background is breathing.