When the scientists are about to project an image using the Martian lens, there are two separate shadows from the boom and mike. As soon as the projector screen is pulled down there is a shadow from the boom that goes across the entire screen. At that same moment, the shadow from the mike can be seen on the wall to the left of the projector screen.
The narrator incorrectly pointed out that Jupiter is a rocky molten lava planet with extremely high atmospheric pressure. What he was actually describing was the characteristics of the planet Venus - Jupiter has no surface. Also, Mars' nearest neighbor is actually Earth, not Jupiter.
One of the reporters refers to a Martian attack on Rangoon,
India. Rangoon (now Yangon) is in Burma (now Myanmar), and while Myanmar had been governed as part of India under the British Raj, it achieved independence in 1948.
When Dr. Forrester and Sylvia and are trapped in the farmhouse, he uses an ax to chop off the electronic eye, and the eye falls apart. However, a few seconds later, when Dr. Forrester lifts the eye, it's intact and clean again.
After the heat-ray tries to shoot down the air force plane, it makes a sweep across the area clockwise. However, when everyone is jumping into the ditch, the fires are starting as though the heat-ray is moving counterclockwise.
When the towns folk first go out to the first landing, Van Buren and Forrester are seen talking. The mechanic is shown walking down into the meteor slide and the towns folk are standing along the ridge, including Van Buren and Forrester. But after the mechanic hits the meteor with his shovel and then scampers back up the ridge, the two are seen walking toward the ridge line.
After the army retreat from the first major Martian attack, Forester and Sylvia are running and find a plane in which they escape. When they enter the aircraft, Sylvia is carrying a purse that she didn't have anywhere else, before or afterward, in the film.
During the street-panic scene in downtown Los Angeles, as Dr. Forrester frantically inquires about the Pacific Tech trucks, his face is bleeding and bruised. After running across some deserted streets, another close-up shows his face is clear. Later on, he's shown with bruises on his face that aren't bleeding.
When the mob hijacks Forrester's truck, he runs over to a couple of MPs and says to the one standing, "They've got to be stopped. Those instruments!", then turns to go. As he starts to leave, the MP clearly begins to follow him, but in the very next shot of Forrester fighting his way back to the truck, not only is the one MP not behind him, but both MPs have completely disappeared from the scene.
When Sylvia and the Doc are in the farmhouse and the Martian ship lands and hits the house, the refrigerator falls over - there is no refrigeration unit on the bottom, just an empty hole and there isn't any electrical wire connected to a plug anywhere.
A number of times the learned Dr. Forrester refers to the object that has landed as a "meteor". This is an appallingly egregious faux pas on his part, as he would surely know that once a meteor hits the ground it is called a "meteorite". Any professor who refers to the bell jar shaped shields that protect the invaders as "protective blisters" would never make so careless an error...
As the radio reporter records his report on a tape recorder, he says that radio doesn't work anywhere, yet the bomber's run is monitored on RADAR. RADAR uses radio to do its work. If radio doesn't work then RADAR would not work either.
Forrester discovers that the meteorite is radioactive by using a Geiger counter. The rate of the counter's clicking increases when the Geiger tube is pointed at the meteorite, but Geiger tubes are not directional. While bringing the tube nearer the meteorite would increase its count range, merely changing the direction at which it was pointed, would have no effect.
When Dr. Forrester and Sylvia meet and talk for the first time, he is wearing red glasses. During the over the shoulder shot in Sylvia's direction it is obvious that there is plain glass in Forrester's frames, as the background and people passing behind the glasses are not distorted as they would have by an optical lens.
When the first Martian space craft lands it is so hot that it causes fires to break out in the area. When the later spacecraft crashes into the farmhouse, the wooden structure doesn't burst into flame.
Modern viewers often complain that the wires used to suspend the Martian war machines are plainly visible throughout the film. The film was originally shot in three strip Technicolor, with prints made using a dye transfer process that resulted in very saturated colors, but with a slight reduction in overall resolution. This reduction in resolution "fuzzed out" the wires in original prints, making them effectively invisible. Later prints were made in Eastman Color, which uses a photographic process and yields sharper prints, but here had the side effect of making the support and electric wires plainly visible - the models had electrical wires as the side pods of the machines really lit up green and the "cobra heads" lit up as well. It is common practice in the film industry to take into account what details will be visible when a print is projected so as not to waste production time and money on details that will never actually be visible to a viewing audience, especially in the areas of effects and matte paintings. Thus, the filmmakers never thought the wires would be visible and in fact they weren't until the first Eastman Color prints of the film were struck in the late 1960s, and they have become even more visible on modern video releases as there is no dye sublimation resolution loss when making video masters from the original negatives.
The reporter records a description of the events on magnetic tape, even though we know that the heat ray generates a magnetic field that would destroy the recording. But there's no reason to believe the reporter knew this, and no evidence that the tapes are ever played back.
At the square dance social, everything electronic seems to have stopped working, including a hearing aid, telephone and wrist watches. The next cut away shows a police car pulling up with the siren sounding. Cars run partly upon electricity (to turn the engine over) and would not work. In addition, the siren would not work.
While electronic devices use electricity to operate, not everything that uses electricity is electronic. This is certainly true of automobile starting systems of the era. Since the system was quite simple and isolated in the vehicle, it's possible that it might remain unaffected. Electronic devices were not that common in the early fifties.
The radio reporter records his final lines into his tape recorder. Sylvia and Clayton comment to each other on what the reporter has just said. Yet they are 30 to 40 feet away from the reporter, and nowhere near him. Additionally, there is a lot of hustle and bustle going on between where Clayton, Sylvia and the reporter are standing, so they should not have been able to hear what the reporter said.
(at around 24 mins) A news reporter is describing what he's seeing as he looks in the distance at the site of the alien "meteor." Suddenly there's a bright green light, obviously from the aliens, but the actor (evidently as a reflex) looks up and to his left in the direction of the off-camera light source, and then quickly back to the aliens.
When Dr Forrester enters the first church looking for Sylvia, the doors close behind him automatically. But the door was opened wide enough to show a lack of a pneumatic door mechanism, the only device available in the 50's that could close a door that heavy.
When Forrester is flying the Army plane he and Sylvia found, he's shown (from the pilot's point of view) nearly hitting a tree. The camera then cuts back to him and Sylvia as he steers the plane, then again shifts to the pilot's view as he veers past a hill with the Martian machines suddenly on the right, then steers left toward another tree, which he crashes into - and which is obviously the same shot of the same tree he had been shown almost striking a moment before.
The goof items below may give away important plot points.
As a trained scientist of the 20th century, Dr. Forrester would be aware of the germ theory and the potential for the transmission of deadly micro-organisms between the aliens and humans. Yet, he touches, directly with his hands, both the alien electronic eye, and the Martian's arm protruding from the saucer hatch, without even wearing gloves as a safety precaution.
In the last scene, in the close shot of the war machine's open hatch, one clearly sees the Martian's arm creep slowly across the hatch itself. However, in the reverse angle wide shot through the underside of the war machine of people approaching the Martian, instead of creeping along the hatch, the Martian's arm and wiggling fingers are seen stretching straight out horizontally from the hatch opening, virtually touching the underside of the ship.
Intellectually, the aliens are clearly much more advanced than human civilization and have seemingly conquered the incredible complexities of interstellar/interplanetary travel. With all their apparent intellectual superiority, isn't it rather odd that they did not consider the obvious possibility (extreme likelihood?) that Earth would harbor microbes adverse to their health?