Boom mic visible: Shadow sweeps over the old man dying as he gasps his last words.
Audio/visual unsynchronized: A jet plane lands with the sound of a propeller-driven craft.
Continuity: Because of budget restraints, one shot of the monster smashing a model car is repeated no less than three times.
Continuity: The shots of the police car rushing to Bickford's house in the middle of the night show a 1930s model car with only one person inside. When the car arrives at Bickford's it is a 1950s model with two men inside. The same shot of the '30s car with one man is repeated later in the film, but when it arrives at the riverfront it too has changed to a late '50s car, now carrying four men.
Continuity: In the establishing scene on board the ferry just before the monster attacks, the little girl with the doll is first seen sitting on a bench in the middle of the deck, then from above sitting along the ferry's port side, then back again in the center bench. Several other passengers switch positions in various shots as well.
Continuity: When the monster is about to attack on land, a man runs toward the camera wearing a dark trenchcoat. When he runs up to the police in the next shot, the trenchcoat is suddenly light colored.
Continuity: Just before the monster first appears on a city street, a car drives onto the street and is stopped by the crowd. When the monster appears, the driver opens the door and runs away. A few moments later, in a close-up shot of the car, the driver opens the door and runs away a second time. The same car (license plate 911 MMF) is seen a few minutes later abandoned on an entirely different street.
Revealing mistakes: When the monster walks through the first city street, one shot shows people running away between several cars and a bus, with a matte shot of the monster walking behind the bus. But in the matte the monster's legs are not seen through the bus's windows.
Continuity: As the monster walks through the city, it stops at the corner of a building and roars down at a group of people below. In the next shot, people are seen running away from the monster as it again walks through the city, immediately after which the monster is shown once again standing at the same building corner.
Continuity: Close-ups of the behemoth rampaging through London repeatedly show it passing by the same building.
Revealing mistakes: In several scenes of the crowds running from the monster, bystanders are visible watching the action while standing around on the sidewalks.
Continuity: The monster is shown rearing up and crashing through Westminster Bridge into the river near Big Ben. A few minutes later, a helicopter flies over the same site, with the bridge again intact.
Continuity: When the monster attacks the mini-sub, the close-up plainly shows the head of a completely different creature.
Continuity: The helicopter that explodes is not the same type of helicopter that was seen a couple of shots before.
Crew or equipment visible: When the behemoth is pushing the ferry, the supporting, floating platform that the model of the monster was nailed to, can be seen at the left side of the frame.
Factual errors: The American title, "The Giant Behemoth", is redundant. Since one of the definitions for "behemoth" is "giant", what the title is actually saying is "The Giant Giant."
Continuity: When the paleontologist Dr. Sampson walks toward the archival cabinet, all the drawers are closed, but when he arrives there, one of the drawers is already open.