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: In the final football game scenes ( from about three-quarters of the way through the film or so) all the spectators are wearing 1970's clothes and have 1970's hairstyles.
Continuity mistake: About half way through the movie, the three main characters are in a loft. When the Asian girl grabs the postal worker's jacket, a cassette tape falls out of his pocket. As the girl bends down to pick up the tape, the camera shows here reaching with one hand, and then the camera switches to a close-up of her picking up the tape with the opposite hand.
Continuity mistake: When Stallone and Williams are on the back of the train, Stallone smashes the window. Cut to Hauer. After this, the window is shown again, and the hole in it is larger than it was when broken.
Other mistake: Towards the end, Capt Williams blows up some buildings (or caravans) to try and stop Hart from continuing, and flies off. When Hart later stops, the same buildings are blowing up again. One could argue that it's being seen from a different perspective, but in the wide shot after Williams flies off, the car cannot be seen.Gavin Jackson
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.
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.