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.
Continuity mistake: As Miles and Sally drive away from the train station her hand is resting on the passenger side window. In the very next shot her hand is by her side. (00:03:40)
Factual error: The aliens request a meeting with Dr. Marvin on the shores of the Chesapeake Bay, near Washington DC. However, the shot of him driving along the shore line shows mountains in the background, which don't exist in Eastern Maryland. (00:35:13)
Continuity mistake: There is a "No Riders" sign that keeps appearing and disappearing on the window of the jeep, from one scene to another, fron shot to shot, throughout the entire film.
Visible crew/equipment: At the climax, when the creature escapes and begins throwing furniture around, you can clearly see the wires attached to the pieces of furniture.
Continuity mistake: When Luther Blair rescues Captain Larson from his cell towards the end of the film they are both shown exiting the cell with pistols drawn and ready. When the shot cuts to the corridor outside both their pistols have now disappeared from their hands.
Factual error: During the meeting concerning Godzilla, one of the scientists incorrectly states that the Jurassic Period was 2 million years ago. The Jurassic Period lasted from 180 to 135 million years ago. (00:29:40)
Continuity mistake: After his meeting with Julia, Winston at home opens the drawer and in a close-up pulls the diary out from under a stack of papers which he lifted with his left hand. The angle changes, and his left hand is on the edge of the drawer, and not supporting the papers any more, nor any paper is visible. There's also a pen on the table that should have been visible before, but wasn't there. (00:36:25)
Continuity mistake: During the opening conversation between Butcher and his lawyer, the shadows on Lon Chaney Jr. switch place depending on the angle - in the shots with the camera behind him, the bars cast a shadow on his neck and side of the head that is not there in the frontals. (00:01:30)
Other mistake: When the title card is shown, the copyright year is shown as 'MCMXXXIV' (1934). It was released in 1956 (MCMLVI).