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: When the mice are feeding the cat, the cat sits up and a mouse passes through his head.
Revealing mistake: In the explosion of the opening scene it is apparent that cut scenes have been shot with several hours time difference because the sun has moved. This is best visible in the reflection of sun in the helmet and shadows of the vehicles in the background.
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: 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: 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 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: 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: A blank firing adaptor (BFA) is visible on the muzzle as the men set up the .30 caliber machinegun.
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: In various scenes before the Compass Rose is supposed to be fitted with radar, it's obvious the 'lantern' round the already fitted radar aerial has been removed and the aerial itself covered with a tarpaulin to simulate the ship in its earlier, pre-radar, state.
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.
Revealing mistake: During the Flak attack on the B25s Arfy notices Orr's plane going down. The scene cuts to a smoking plane going down at a steep angle, but you can see the plane was flying straight and the film turned at an angle as the colors on the horizon are also at a steep angle.
Revealing mistake: Right at the beginning of the movie, an alien blasts Lieutenant Smalls and he drops his rifle. The weapon wobbles, revealing it's a rubber prop rifle. (00:01:55)
Revealing mistake: Whenever our heroes are shown firing the Vickers guns on or off the vehicles, they are very obviously fitted with blank-fire adapters to the front. The belts of ammunition for them throughout the film are also blanks - the cases are visible, but the bullets that should project out the other side of the belt are not present.
Revealing mistake: Most of the tank battle scenes throughout the movie are low budget CGI.