Because of budget restraints, one shot of the monster smashing a model car is repeated no less than three times.
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.
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 1930s car with one man is repeated later in the film, but when it arrives at the riverfront it too has changed to a late 1950s car, now carrying four men.
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.
Close-ups of the behemoth rampaging through London repeatedly show it passing by the same building.
At the conference at the opening of the film, a delegate says the atomic tests occurred in the "most uninhabited spot of the globe". In reality, the occupants of Bikini Atoll (where these tests took place) were relocated three times to other islands.
The admiral tells Prof. Bickford and Karnes that the Thames is completely guarded by radar and that they can even see the fish, noting that nothing can get by the radar. However, radar uses microwave radio frequencies about a centimeter in length and microwaves are strongly absorbed by sea water within a few feet of transmission. Whilst the radar can see a destroyer and, later, Dr. Sampson's helicopter, it would be virtually useless underwater.
In the scene when Karnes is on the boat searching for the creature, he is using the wrong type of equipment.
The creature is supposed to be radioactive so Karnes should be using a geiger counter. Just before the monster is spotted, there is a close up of the device. It's a milliamp meter which measures electrical current, not radioactivity. The face of the gauge should be labeled R/Hr (roentgens per hour) not milliamperes.
At this point in the movie, it isn't known that the creature can emit electricity.
The creature is supposed to be radioactive so Karnes should be using a geiger counter. Just before the monster is spotted, there is a close up of the device. It's a milliamp meter which measures electrical current, not radioactivity. The face of the gauge should be labeled R/Hr (roentgens per hour) not milliamperes.
At this point in the movie, it isn't known that the creature can emit electricity.
In the radio report for the missing vessel Valkyrie, it's described as a steamship, which is a passenger vessel, but the subsequent shot of the wrecked ship beached shows a freighter, not a steamship.
Karnes asks for transportation back to London. The next shot is a single-seat Hawker Sea Hawk jet fighter that is making the sound of a propeller-driven airplane.
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." The word 'behemoth" comes from the Hebrew word for beast, so the title would be "The Giant Beast".
In the picture the police deliver to Professor Bickford, the Behemoth's footprint completely dwarfs a police car (the whole car could easily fit within it), yet, during the monster's rampage through London, when it steps on a similar-sized car, its foot cannot completely crush the vehicle. Had the foot been as big as its footprint, it should have been like a shoe stepping on a cockroach.
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.
In several scenes of the crowds running from the monster, bystanders are visible watching the action while standing around on the sidewalks.
The naval officer in the radar center says that, because of the fog, it's unlikely Dr. Sampson and his helicopter will see much of anything. However, exterior shots of the helicopter reveal a mostly clear sky, with just a few clouds.
When Karnes and Bickford first visit the fishing village, they can be seen standing in first position on the pier for at least two seconds before walking toward the fisherman - obviously waiting for an "action" call.
When Karnes finishes dissecting the fish, which he suspects might be contaminated by radiation, he washes his hands in a nearby sink. However, a moment earlier, he takes his pocket knife, which he has been using to cut the fish, folds it and puts it back in his pants pocket without wiping it off or cleaning it.
When Dr. Sampson learns that the dinosaur is still alive, he assumes that it must be in the Pacific. When told by Prof. Bickford that the creature is off the coast of England, Sampson says it's making for the Thames, where bones of other such dinosaurs have been found. No mention is ever made as to how or why Sampson thought the monster would have been in the Pacific. In fact, no mention is made of where the Behemoth was irradiated.
Near the end, when the monster picks up and drops a car into the Thames, the wires supporting the car are visible.
When the behemoth is pushing the ferry, the supporting floating platform that the model of the monster was nailed to can be seen on the left side of the frame.
When the Behemoth destroys the ferry, the platform on which the head of the monster is attached is clearly visible coming in and out of the water.
When Karnes and Bickford are interviewing the village doctor, he says: "The man was dying when I got there", but the guy was already dead, long before the doctor could have gotten there.
Shadow sweeps over the old man dying as he gasps his last words.
When the destroyed boat interior is onscreen, by the left wall.
One of the people fleeing the Behemoth is the kid in the black sweater, who was killed earlier in the film when the monster destroyed the farm.