Three muzzle flashes, one report! In the close-up of the quick-triggered soldier atop the tank turret, we see and hear him fire his pistol, but for the sharp-eyed, the wide-shot of the tank crew that follows, reveals the visible but silent muzzle flash of both soldiers' side arms.
As pointed out in an earlier Goof, H.V. Kaltenborn refers to "the beautiful spring weather", whilst later on, the tag on the suit Klaatu has "borrowed" shows the date 7-18-51. Bobby, at one point, asks his mother if he has to go to school tomorrow, and later there's another reference to his being in school. Unless Bobby has been flunking out and is attending summer school, he would not be going to school in July.
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". (However, Klaatu's method could work. e.g. To divide 1/3 by 1/4 find the common denominator and re-express as 4/12 divided by 3/12. Then simply divide the 4 by 3 to get the answer: 1 and 1/3. Ten out of ten for alien mathematics!)
As Klaatu is descending the ramp from the spaceship, and makes it onto the grass, he reaches for the metallic device that could help mankind understand the other planets, and people. Once Klaatu clicks the device open, he's immediately shot and the device flies out of his hand as he collapses onto the ground. Although it looks as if the shot hits Klatuu's hand and device, the actual wound appears near his shoulder.
During the montage shots of newspaper headlines during the hunt for Klaatu, a photograph shows him still standing on his ship holding out the viewing device which was shot out of his hand. During the earlier scene of his emergence from the saucer, he didn't produce the device until leaving the ramp and approaching the onlookers.
Bobby's room is clearly shown to be at the top of the staircase, and Helen's room is down the hall. However, in the shot where Helen is seen getting her coat from her room to go out with Tom to the movies, the top of the staircase can be clearly seen just outside of her door when it should be down the hall and much farther away from her room.
In the scenes showing the arrival of the military, Klaatu's injury and the eradication of the weapons, the shadows of the military equipment, spaceship and actors change radically. The first shadows shown of the tanks are long as if the time of day were, either, very early morning, or, more likely, late afternoon. Then when Klaatu leaves the spaceship, he throws a fairly short shadow, such as one showing within an hour or two of noon. The tanks and Gort also show the short shadows. When Gort starts to destroy the tanks and weapons, the shadows are still indicating that it's perhaps 2pm. When he finishes, a few moments later, the shadows are long and drawn out, like they were at the beginning of the scene. In movie time, no more than 10-30 minutes have passed, whilst the shadows say it's more like half a day.
When Helen and Klaatu are going to the professor's, the army states that their cab is heading northwest on Connecticut at Columbia Rd. The cab then passes under the Dupont Circle underpass on Connecticut AV. The underpass is south of Columbia Rd, not north. Also, if the professor lives near the State Department, they are going in the wrong direction. The State Department offices are south of Columbia Rd.
As the spaceship races across the world, scenes of successive radio announcers (or people listening to them) are shown, apparently in order of their broadcasts. When the BBC announcer in England is shown delivering his broadcast, the clock behind him reads 8:33 (p.m.). The next shot shows radio commentator H.V. Kaltenborn doing his broadcast from Washington, D.C. The clock behind him reads 3:24. Since Washington is five hours behind London, and assuming the broadcasts were indeed shown in order, Kaltenborn's clock should have read no earlier than 3:33, and probably a minute or more later than that.
Just after Klaatu is shot and is in the hospital, he is visited by a government official. Klaatu states he has traveled "Five of your Earth months" and "250 million of your Earth miles".
250 million miles would put his starting point between Mars and Jupiter, depending on when you measure. At the far end of the scale, Mars itself can get 250 million miles from Earth.
Not all vehicles would have been stopped by the power outage.
Diesel-engined vehicles, particularly at that time, don't need electricity to run.
This would also explain why a boat can be seen moving in one shot.
When Klaatu visits Dr. Barnhardt in the evening, there is a small piece of paper pinned to one side of the blackboard, the left side. On the paper is seen (briefly) "Do Not Erase". A few moments later in the same scene, there is no paper pinned to the side of the blackboard. Again, in the same scene, the paper is back very briefly, but just as before, disappeared almost immediately.
Bobby and Klaatu visit the grave of Bobby's dad. Whilst still at Arlington National Cemetery, they decide to go to the movies that afternoon. That evening, back at the boarding house, Bobby tells his mom "we went to the movies, and got ice cream cones, and then we went to see Daddy".
In some long shots of Gort walking, wrinkles in the legs of the costume are clearly visible. However, it could be argued that, coming from another planet, Gort is made from a very flexible kind of metal that is completely unknown on Earth.
In the boarding house scene, Drew Pearson states that the only means of identifying Klaatu are the photographs taken outside the spaceship, in which his head is covered by a helmet. However, Klaatu had also spent three days at Walter Reed Hospital, and any of his caregivers could have provided authorities with a detailed physical description.
When Klaatu asks Mr. Harley if he could speak to the United Nations about his mission, Harley allows that they could call a special session of the General Assembly, but warns Klaatu that "The United Nations doesn't represent all the nations," after which he and Klaatu completely abandon the idea of using the UN as a forum. However, the UN has always allowed observers from non-member states and organizations to attend its sessions (though they may not speak or vote), so there was absolutely no reason why the UN could not have been used for such an extraordinary purpose as hearing Klaatu's proposals.
Helen displays a complete lack of parental concern as she allows Klaatu, going under the name of Mr Carpenter, a strange man who simply shows up at the boarding house the night before, who shows no identification to anyone, to spend the day with Bobby, her underage son. She even tells Carpenter how nice it is for him to suggest it.
In the shots from behind of Gort carrying first Helen, and later Klaatu, into the spaceship, the people being carried are clearly either small adults or adolescent children dressed to resemble Helen and Klaatu, in order to give the illusion of greater size to Gort. The small size of their limbs, and the differences in their relative heights and appearance from the close-up shots of Gort carrying the actual Helen and Klaatu, make this obvious.
At the beginning, H.V. Kaltenborn mentions the 'beautiful spring weather' in the Nation's capital, but we find out later that it is July (Klaatu sees a dry cleaner's receipt on his suit dated 7-18-1951). In spite of the spring and summer references, when Klaatu and Billy walk around Washington, many of the trees are still bare as they had yet to regain their leaves. (Filming had started early in the year.)
After Klaatu is shot, blood is seen on his shoulder, but when he's actually shot, not only is there no sign of his being hit in the shoulder, the device he's carrying is blasted out of his hand, and his physical reactions clearly are those of someone just shot in the hand or wrist. Not to mention that the device is found shot apart, damage that could not have happened to it just from falling onto the grass, and had Klaatu been hit in the shoulder.
When Gort goes to collect Klaatu, he passes Helen as he walks to the door of the central room in the spaceship and what looks like a large tear can be seen in the front of his otherwise solid looking left leg.
When Klaatu returns to the ship at night to contact his people, Gort is shown from the front after he knocks out the two soldiers. There is no cut-away as Gort turns to open the ship's ramp for Klaatu, and the zipper in the back of the rubber suit can plainly be seen as Gort walks towards the ship before he turns around to face front again.
When Gort begins marching down the ship's ramp at the beginning, a shot shows the crowds running away in panic. The shot is clearly a speeded-up film of the crowd, most of whom were plainly walking away from the scene rather leisurely. Also, when the shot switches back to the retreating military men, the crowd can be seen still standing behind them, not having moved at all.
When the spaceship (seen as a glowing white disc) is tracked across the sky in Washington, D.C., it passes a flagpole atop a building. As the ship is supposed to be in the background, the flagpole should remain in full view as the ship passes behind it, but a close look shows that the disc briefly blots out part of the pole as it passes (due to an error when the disc was optically printed onto the film). The effect makes it seem as if a tiny ship had just passed in front of the flagpole.
After Helen tells Gort "Klaatu Barada Nikto", he picks her up and carries her to the ship. There were only two Gort suits. One laced up the front for back shots, the other laced up the back for front shots. This scene used the one which laced up the front. Since Gort is shot from the side, very briefly you can see the laces up the front where Helen's hand is against his chest.
The goof items below may give away important plot points.
Klaatu is shot in his left shoulder, yet we see him wounded on the ground and leaning against his left side with his left hand on the ground. That would have been too painful and, instinctively, Klaatu would not have leaned on the side he was shot.
When Gort picks up Helen, she is wearing shiny black high-heeled shoes. In the scenes immediately before, such as when she had knelt down by Klaatu's side after he had been shot, she was wearing low-heeled matte finish shoes. Of course, she would not have had time to change her shoes.
A photograph shows the famous publicity still with Gort to the left of the photo and helmet-clad Klaatu to the right and slightly behind his robot, waving at the crowd. This never happened: Gort only came out after his master was shot down, therefore at this point in the movie, both aliens were not seen together on the vessel for that photograph to be taken. Additionally, at the end of the movie, Klaatu is not wearing his helmet when he waves goodbye to Helen and Gort has long disappeared inside the spaceship. However, this being the 1950's, the current journalistic "truth in media" standards had not yet been adopted, so it is entirely possible (in fact, probable) that the newspapers simply took various photographs of Klaatu, the gizmo in his hand, Gort and the space ship and com-posited them together to produce the image used. This was a widespread and accepted practice among newspapers at the time (most notoriously in the 1920's) and whilst very few respectable, mainstream newspapers resort to such photo tampering, even today tabloids like The Weekly World News still employ similar methods.
When Gort moves behind the wall to pick up Helen, the frame shifts slightly. This was because director Robert Wise stopped the camera, moved in a rig to hold Patricia Neal and started again as (Lock Martin could not do it on his own - see trivia).