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.]
Factual error: When the Titanic sinks all six dwarves and Kevin end up in the sea clutching a lifebelt. The water in which the Titanic sank was freezing - that is how most of the casualties died, by freezing, not drowning. In water like that you'd be lucky to stay conscious for more than a few minutes. Despite this none of them show the slightest effect of the cold. Maybe the dwarves have some 'magical' ability to withstand lethal cold, but Kevin doesn't even react to being plunged into freezing cold water. He'd be screaming in pain, but he doesn't even show the slightest sign of discomfort.
Plot hole: Bond makes a huge tactical error after diving to the St. Georges. He knows the Russians and their operatives are after the ATAC. The ATAC itself is expendable to Britain, since it has a self-destruct mechanism that, under proper procedure, would have been set off when the ship sank. So why is Bond trying to retrieve it? Because he disarms the self-destruct, he actually allows Kristatos to get his hands on it, forcing Bond to track it down again and, to stop the Russians from getting it, HE DESTROYS IT! So why doesn't Bond, instead of disarming the self-destruct, set a timed charge or toss a grenade in the room to destroy the ATAC while it's at the bottom of the sea? The answer is, of course, that if Bond destroys the ATAC before the bad guys can get at it, the movie's over. Even so, at the end, when Bond finally does destroy the ATAC, he tells Gogol it's "detente. You don't have it. I don't have it." Clever line, but it reinforces the fact that the British don't need it. They can build another one.
Visible crew/equipment: A stock car carrying Mel Tillis and Terry Bradshaw drove into a hotel swimming pool. If you watch the car as it drives into the pool, you'll see the jump ramp built at the end of the pool.
Visible crew/equipment: When Wez rips the door off the tanker you can see a crouched crew member next to Max. This has been disputed but it is there, watch underneath the steering wheel just after Wez starts shouting "Go! Go! Go!". (01:19:05)
Continuity mistake: When Snake kills the wrestler he falls forward shoulders forward, next minute his arms are over the ropes, next minute his arms are in a different position again - quite active for a dead man. (01:16:55 - 01:18:10)
Audio problem: During the climax of the film, the maiden takes the stone from Galen and attempts to smash the amulet. Galen pulls the stone away and says "NO! He said I'd know the time". However, his lips do not match the words. He appears to say "NO! It is not yet time!"
Revealing mistake: At the beginning when the ruler is making his speech, you can see his modern day fillings in his upper molars.
Visible crew/equipment: After Arthur drinks from the Grail and goes to visit Gwinevere at the convent and she gives him the sword back, he paces around her chamber- you can clearly see the film crew reflected in his armor.
Continuity mistake: When Albert Johnson jumps into the top of a tree, he first throws his backpack off the hill but leaves his rifle. After he gets to the base of the tree both his backpack and rifle are there.
Revealing mistake: When Joe has died of blood poisoning there is a close up of his head and neck, you can see him breathing and his eyes flicker.
Factual error: Franklyn Hart keeps his car running by pumping out the gas from the bottom of abandoned gas pumps which the pumps themselves couldn't reach. In reality, as this gas is on the bottom, it would be full of sludge and garbage, and since it has been sitting there for 20 years, it would barely be usable and would probably damage the engine. He certainly wouldn't be able to do high speeds with it.
Continuity mistake: When Chuck Norris is battling with the Triads at Mako's house, a oriental box is knocked off a table in the first shot when a Triad is slammed against the table it is on. In the next shot of the table, the box is back in its' position.
Factual error: There could never be an aircraft of World War 2 vintage with the call sign "Yankee Zephyr". If it was a US aircraft (it appears to be) it would have the call sign "Yankee Zulu". If it was an RAF aircraft it would be "Yoke Zephyr". This all changed when the phonetic alphabets were standardised by NATO in the Fifties, but the DC3 in this film is supposed to have crashed before the end of World War 2 in 1945.
Revealing mistake: During the final battle one of the bad guys is blown through the air due to an explosion - but right behind him you see the springboard used to launch him.
Continuity mistake: Near the end of the movie Jane's wearing a loin cloth like Tarzan that the natives dressed her in. When she's with Tarzan and a monkey after washing off the white paint she's suddenly wearing a skirt.