Continuity mistake: In the scene towards the end of the film where we see Slade's body fall, it falls onto a submerged rock just below the surface of the water and there is a splash of water. In the next shot Tarzan looks down from the cliff above and Slade's body is on a large dry rock, a little distant from where the body originally fell.
Revealing mistake: When Bela Lugosi walks off screen, it's obviously a freeze frame. The swaying tree stops moving and even though he was hit by a car, his shadow is still visible. (00:07:55)
Revealing mistake: In the shooting scene in the Mount Rushmore cafe, a boy in the background puts his fingers in his ears, because he knows the gun is about to be shot.
Factual error: Towards the end when the cavalry uncovers the American flag, it has 50 stars.
Revealing mistake: During the chariot race, where the contestants are riding towards the screen, tyre tracks from the camera vehicle are clearly visible imprinted in the sand. (00:20:50)
Continuity mistake: The escape train stops at a station at which another train has been the site of a massacre. One of the victims of this massacre has his head leaning out of a railway carriage window. As Kenneth More and Lauren Bacall from the escape train walk about the station, he can be seen raising and then lowering his head again as he realises that the 'take' is not complete.
Factual error: Iceland sure looks a lot like the California desert.
Continuity mistake: The background shots of the Matterhorn show it with a clear sky, then a cloud around it, then a clear sky again. This keeps happening.
Factual error: Karnak was an Egyptian city, not one of their gods.
Deliberate mistake: For all exterior shots on the surface of Mars, the crew's "pressurized" space helmets have no face-plates (their faces are fully exposed to the hostile Martian environment). The transparent face-plates they intended to use reflected far too much studio set lighting, such that the glare would have obscured the actors' faces. On a $200,000 budget and a 10-day production deadline, they simply scrapped the face-plates and shot the scenes with wide-open helmets.