Factual error: When Bobby is doing his math homework, Klaatu looks over his shoulder and says: "All you have to remember is, first find the common denominator, then divide." Division of fractions doesn't require a common denominator. In fact, the original script says "subtract".

Visible crew/equipment: When Gort picks up Patricia Neal next to the flying saucer, you can see cables leading down to her body to keep her hoisted.

Revealing: When Gort goes behind the wall to pick up Patricia Neal, the camera moves about an inch in the same shot, because they had to stop filming, go rig the wires up to Patricia, then start filming once again.

Plot hole: The military's security is ridiculously inadequate. After Gort subdues the only two GIs guarding him and the spaceship, the military encases Gort in solid material, but later still only two GIs guard him and the spaceship when Patricia Neal arrives. With a development of this magnitude the US military would probably seal off the city.

Continuity: When Klaatu writes some notes on the blackboard, in order to help Professor Barnhardt, the handwriting of the words on the board changes between shots, most noticeably the 'T' on 'Try.'

Plot hole: Klaatu is shot and his body is lying in a prison cell. Gort leaves the flying saucer and walks all the way to the heavily guarded police station in downtown Washington DC. Gort is 8 feet tall and is a robot plus he uses his noisy death ray to create a hole in the police station to retrieve Klaatu's body and nobody noticed him? On top of that, he walks all the way back to the saucer unseen with a dead body.

Continuity: During the news broadcast, the TV announcer is evenly lit. You can see this in the side view of him, as well as on the TV monitor that's next to him. Then, just after he says "there is no reasonable cause for alarm," the microphone in front of him is suddenly casting a big shadow on him.

Continuity: In the very beginning of the movie broadcasters around the world are commenting on the mysterious spaceship. To lend a bit of calm and normalcy one broadcaster notes that despite what is happening many people are enjoying the fine spring weather in the Capital, to this end picnics and the wonderful cherry blossoms are plainly depicted. Shortly afterward when Klatu leaves the hospital, he is seen examining the cleaner's tag on the suit he "borrowed". This is where he adopted the name Carpenter. Clearly printed at the top of this tag is the date-7/18 1951, not spring by at least a few months.

Continuity: The taxi Helen gets into changes in one shot as it drives down the highway, evident by the writing on the side, then back again when it parks outside her house.

Revealing: During the black-out, there's a shot when you see two cars moving in the background. One of them is slowing, which is normal if the engine stops, but the other is parked and then starts moving.

Revealing: When Gort begins to walk down the saucer ramp, after Klaatu is shot, the crowd gets scared and runs away. I guess the director found the extras running too slow so he sped up the film.

Revealing: After all of the elecrticity is neutralised, in a street shot you can see neon signs are still working; a huge Coca Cola one, for example.

Continuity: When Gort emerges from the spaceship, we see all of the crowds run away in fear and panic. Yet in the very next shot the crowds are visible standing behind the ropes again.

Continuity: Klaatu introduces himself to the Professor for the first time by relaying some details of his stay at the hospital to verify who he is. Klaatu tells the Professor he was staying in room 309, but the early scenes at the hospital show him in room 306.

Continuity: In some shots, Gort the robot has air vents under the chin. In others there are no vents.

Continuity: As Drew Pearson is doing his news broadcast, the desk next to the microphone is clear. In the next frontal shot, two pencils have appeared next to the left of the microphone.

Continuity: When Klatu goes to see the professor, there are several white notes tacked around the chalk board. In later shots some of the notes are gone.

Continuity: In the newspaper headlined 'Step up Hunt for Spaceman' the photo on the right shows Klatu and Gort on the hull of the ship. This shot is a still from the end of the film.

Revealing: When the spaceship arrives in Washington, many people look in the wrong direction.

Continuity: When the power goes out there is a scene where it shows all the cars not being able to work, although in the background there is a movie marquee with the lights on.