When the four characters are in the saucer, the police officer takes his gun out and shoots it. The sound effect comes too late to cover the "click" of the actor firing the prop gun. If he had actually fired the gun, the sound of the discharge would have covered the "click" of the mechanism.
During the final clamactic battle in the skies over Washington, there are several shots of Dr. Marvin speaking into a hand-held microphone. You'll notice as his lips move that what he is saying clearly doesn't match the dialogue heard.
During the opening sequence, just as Marlowe is nuzzling Taylor's neck while she's driving, the rear-projected film behind them indicates not only that Taylor is driving quite fast, but that her car is also passing another on the two-lane highway. Taylor's actions and demeanor in no way indicate such a critical maneuver.
In the first scene after the introduction, in full daylight, Russell remarks to Carol that they have been "married two hours." In the next scene, later the same day, she tells her father that they got married "last night."
When the aliens destroyed the navy ship, they gave the location as a longitude and latitude with no reference to north/south and east/west. Without these directions, those two numbers could describe four different points on the globe.
While overall levels of solar activity do have an effect on climate over the long term, and a major disturbance in solar activity would affect weather, it is certainly not correct, as stated, that simple sunspot activity has "a direct effect upon our weather."
When rocket 12 is being readied for launch, a Redstone rocket (state-of-the-art in 1956) is seen on the launch pad. However, after the saucer-men's attack, the rocket shown burning is an old WWII era V-2.
During the offspeed playback, the reels are turning at close to normal speed, certainly at least half normal. For the high-pitched sound we heard earlier to have concealed an unnoticeable spoken message, the speed discrepancy would have had to be more than a factor of 10.
In the first scene, Dr. Marvin is recording his report on the tape recorder when the saucer appears. As the sound of the saucer becomes audible, he says "Do you hear something? Listen." A moment later after the saucer has "buzzed" the car, he tells his wife "Pull over." However, when they play back the recording, all that is heard is the saucer sound; the two comments are not on the tape.
Just a little past 13 minutes into the movie, as "rocket eleven" is launched, the video monitor shows the rocket release cable dropping at the countdown of 8. At the countdown of 1, the video monitor shows a different rocket, with a new release cable still attached, falling off (again?) as the rocket launches.
When the Marvins stop their car to get out to look at the flying saucer, there's a large sand dune behind them alongside the road, but in the rear-projection shot just before they stop, the terrain along the side of the road is flat.
When Carol and Major Huglin are chasing Marvin through the city streets as he is headed to his meeting with the aliens, he makes a hard 90 degree turn. Carol and the Major make the same turn in pursuit and they're all still in the middle of the city. A second later they pass a motorcycle cop and they're now suddenly out in the country and the city is nowhere to be seen.
When a flying saucer destroys a B-29 Superfortress, a gunner is shown firing from an open gun port in the side of the fuselage. B-29s had remotely-controlled turrets, except for the manned tail gun that was semi-remote controlled. Open waist-gun ports were a feature of the B-17, stock footage of which was used for the climax of the scene.
During the chase scenes, when the saucers are attacking the fleeing earthlings, the footage of a flatbed truck being blown up is repeated in it's entirety after a 5 second cutaway to Russell and Carol in their car.
When the saucer is engaged in combat with the bomber, that bomber is represented as a B-29. When the scene cuts to the bomber's cockpit, it is is not the very open "greenhouse" type of the B-29, but the more conventional type with specific windscreens and looks more like that of a B-17.
Russell makes a tape recording of what he fears will be his last message. He mentions that the flying saucer sound can be found on the same tape, and says he is stopping recording because the machine's battery is running low. For no reason, he then switches the recorder to playback without rewinding. Its off-speed playback then reveals the message in the sound. This means he must have been placing his message on a part of the tape where, if the battery had not run low, it would have obliterated the sound.
When Dr. Marvin is being interrogated by the officials, he complains that they've been there all night and that it's late. The others concur and the meeting breaks up. However, the window in the room plainly shows that it's broad daylight outside, and when Marvin subsequently drives to his hotel (and at one point states that it's now 4:30 AM) it's also clearly daytime.
About 19 minutes into the film, when the three soldiers behind their mortar get disintegrated by the alien ray, a "giant" house fly can be seen for one single frame right above the head of the rightmost soldier. It must have landed on the plate during composition of the effects shot.
In the beginning of the film, Dr. Marvin and his wife are driving in the desert in a Mercury. After the attack on Sky Hook, Dr. Marvin and his wife are on a plane to Washington, DC. Later in Washington, DC, when Dr. Marvin goes to his hotel, he gets out of the very same car that he was riding in, back in the desert.
During the attack on Washington, a saucer fires on what looks like a bell tower with a clock on it and a pyramid-shaped top. However, when the scene shifts to a closeup of the tower exploding, it's Los Angeles City Hall (edited in from The War of the Worlds (1953)).
When the Marvins are trapped below ground after the attack on Skyhook, Dr. Marvin turns on a flashlight once the power goes out. However, whilst the light goes on, it casts no beam anywhere. Similarly, when Marvin later drives his car to his hotel in Washington, its headlights, whilst lit, cast no beams.
In the scene where the destroyer is to be destroyed, the gun mounts are single 5" mounts. When the destroyer is firing her guns, a twin 5" mount is shown. When the destroyer is shown to explode, the actual film clip used is of a battleship exploding.
Some of the streets through which the trucks mounted with the intercepting guns drive were obviously filmed on the studio back lot, as no such neighborhoods or background areas exist in Washington, D.C., where the action takes place.
When Maj. Huglin shoots the alien that has just killed Prof. Kanter, the alien falls forward and it's helmet comes loose, but when they turn the alien over to examine it, the helmet is back on tightly.