Revealing mistake: Halfway through the movie, Alta is swimming in the pond, supposedly nude. However, when she climbs out, she can be seen wearing a flesh-covered swimsuit. (00:45:15)
Suggested correction: Alta never said she was naked. She didn't know what a bathing suit was and Adams assumed she was naked.
Revealing mistake: A couple cross the road to enter Victoria Coach Station, London. There is the noise of a coach braking hard and they throw themselves away from a coach just inside the entrance, which obviously was not moving at the time. They walk into the station and talk to an inspector, while the same coach is driven out of the entrance past where it is supposedly parked.
Revealing mistake: During the interrogation after the Albert Hall assassination attempt, the telephone used is an obvious Western Electric American-made phone instead of a British-manufactured telephone, betraying the fact that the interiors for the movie were shot in Hollywood.
Revealing mistake: The alien is starting to mess with all sorts of mechanical and electronic devices. One of the first ill-effects shown is a large industrial cable reel that is dangling in midair when the mechanical arm lifting it is paralyzed. Problem is, you can see the operator has his hand on the controls and is stopping the crane himself using the lever, nothing alien about that. (00:14:50)