Factual error: The film starts in the year 1936, and just like the RPG Indy uses to threaten Belloq with, the MP40s (or at the earliest, MP38s) are an arms-historical anachronism in this movie. As the numbers in their names imply, the MP38 was first produced in 1938. The weapons in the movie are not the similar-looking ERMA MP-36, you can see the ribbed, vertically angled magazine holders typical for the MP40 - its predecessors had either a 30°-canted, smooth magazine holder (MP36) or a round viewing port for checking the ammo (MP38). (01:31:45)
Factual error: Look to the right of the table lamp, there is a bottle of Myers Rum that has the modern plastic (silver/clear) cap and plastic pour spout. Not 1940s era. (01:33:10)
Continuity mistake: Indy looks at the Wurffler through the binoculars. In the next shot, when he takes them off and looks at Katanga, the submarine has moved to the left and astern. (01:34:58)
Continuity mistake: When Marion arrives on the deck of the Bantu Wind, Dietrich turns to look at her. Katanga is in the background, behind the colonel. But, just before Marion hits Dietrich, Katanga appears on the opposite side from where he was and catches Marion. (01:36:00)
Continuity mistake: In Geheimhaven, Indy watches the submarine hidden behind some ropes. When Marion comes out of the submarine and the camera focuses on the back of Indy's head, the ropes disappear. (01:39:13)
Factual error: When Indiana Jones ambushes the Nazis with the Ark, he threatens them with an anti-tank rocket. This is set in 1936, and anti-tank rockets weren't developed until the American M1 in 1942. The Germans immediately copied it from captured weapons and made their own much larger version known as the Panzerschreck, then Panzerfaust. The Russian RPG which Indy is holding was developed from the Panzerfaust in 1949. (01:41:55)
Continuity mistake: Dietrich asks, "If we refuse?" Next to him stand four soldiers in a row, looking at Indy. In the next shot, the soldier who was holding a rifle is gone, and the two with machine guns are now giving their backs to Dietrich. (01:42:52)
Continuity mistake: When Belloq grabs the machine gun, his left hand is on the trigger and his right hand on the gun cartridge as he turns round with his back to the camera, but in the next shot, his right hand is on the trigger and his left hand on the cartridge but in the next shot, his hands have changed position once more, this time left hand on the trigger and right hand on the cartridge. (01:42:55)
Continuity mistake: In the canyon, in the shot of Toht, just before Belloq says "Do as you will", everyone in the background (Marion and her two guards, Dietrich, some soldiers) is gone (taking as reference the giant stone behind Belloq and the characters' positions in the previous and next shots). (01:43:49)
Continuity mistake: As the Ark is placed on the altar, Toht moves to the left of Belloq. Behind the German, a soldier without cap can be seen filming with a hand-held camera. In the next shot, that soldier has moved to the opposite side of the canyon and is squatting. (01:44:24)
Continuity mistake: Over Belloq's left shoulder and behind Toht, a soldier stands next to a klieg with a machine gun. In the next shot, the soldier's gun has disappeared. (01:44:25)
Continuity mistake: When the two soldiers place the Ark on the altar, they move to the walls of the canyon, and Toht stands next to Belloq. A few shots later, the soldiers are next to the Ark's poles (where they will be in the next shot), and Toht seems to be very huge. (01:44:39)
Other mistake: The Angel of Death attacks the altar and Toht and Dietrich scream because of its revelation, but Belloq, for some reason, doesn't seem to see it. Just before the fire column rises, he's still calm. (01:47:10)
Suggested correction: If you don't know the reason, perhaps you should ask a question instead of assuming it is a mistake. Belloq studied the ark and probably better predicted what might come out of the ark. He is also looking directly into the ark and is mesmerized by what he is seeing, until eventually he does scream before his head explodes. The other two are terrified at seeing the apparitions.
Actually, it's pretty impossible that Belloq studied the Ark. If he knew what would come out of it, he literally committed suicide by opening and watching the Ark open, which doesn't make sense. He believed during the whole movie that the Ark contained the Ten Commandments tablets, not some kind of ghastly things.
He didn't know what would come out, but it doesn't mean that he, like Indy, expected just 2 stone tablets. He expected power, for him mostly.
Revealing mistake: When the Nazis are about to glow (and die), check the one on our left. His shirt is already unbuttoned right where the light will subsequently glow (which was a mere light bulb). A second later, he triggers a device clutched in his right hand (seemingly a switch) seconds before his chest lights up. (01:47:25)
Continuity mistake: While the Holy Fire is killing the soldiers, in a shot of two soldiers being hit by the light, the stone wall is missing in the background of the scene. (01:47:30)
Visible crew/equipment: Right when the Nazis are struck with the light, one soldier shakes wildly and one can see the cable coming out of his trousers and stretching off-screen to the right. (01:47:30)
Continuity mistake: Indy and a Nazi soldier are fighting in the cab of the truck when they come to a place where a stone building is being built. As the truck is driving into the scaffolding, several rocks come down and hit the truck and remove the rack from the top. Moments later the rack is back in place. (02:50:00 - 03:01:00)
Revealing mistake: While Indy and Marion are in the Well of Souls, and they encounter the snakes, Indy falls to the ground only to be confronted by a hissing Cobra rearing its head. Look carefully and you'll see the snake's reflection on the safety glass between it and Indy. Briefly you can also see the torch's reflection while he's waving it around. You can also see Marion's reflection when she falls in later on and is face to face with the cobra. [This has been corrected in the new DVD set. You can only see it if you have the original VHS. I think it's visible in the "making of" on the DVD as well.]
Revealing mistake: After Indy gets behind the wheel of the truck containing the ark, he jerks the steering wheel to the right to run the pursuing jeep off the road. He then jerks the wheel to the left to hit an upcoming motorcycle. In neither case do you see his body sway with the presumably drastic swerve of the truck. Apparently this was filmed in a stationary vehicle, or one in tow that was fitted with a prop steering wheel.
