Richard Carlson's house in the desert has a fireplace on the inside but no chimney on the outside.
Besides not having a stone chimney on the exterior of Putnam's house, the interior sets are much more spacious, and complex than the small "crackerbox" exterior building could hold.
When the posse shoots the alien Frank while driving the truck, he crashes head-on into the rock. But when the next shot shows the burning truck it is facing away from the rock.
The shot of the alien craft flying away from the desert at the end of the film is the exact same shot of it flying across the sky for it's crash landing at the beginning. It has simply been flipped in processing to appear as though it's going back the other way.
Near the beginning of the film telephone lineman, Frank Daylon, is shown working up on a utility pole. However, the pole is clearly carrying only electrical power lines (and not telephone service). So not only is there no reason for him to be on that pole, but it's also not possible for him to hear strange noises over telephone lines which aren't present.
Artistic license and suspension of disbelief notwithstanding, there is a scientific oversight worth noting: the alien's POV is in 3D, despite the fact that it's a cyclops. The otherworldly visitor has one eyeball and one pupil, when it's necessary to have at least two in order to perceive stereoscopic vision.
When John turns around to go back and look for Frank and George, the tires on his car squeal while he's turning around on the sand beside the road. Car tires can't squeal on sand.
After the spaceship has crashed, when they look through the telescope to see the crash site the image is the correct way up but since this is an Alvin Clark refractor telescope, the image should be upside down.
According to the tear-off calendar on the wall in the sheriff's office, around 50:00, the climactic day of the movie was "February 11 Saturday". February 11 was one of the actual days of filming, in 1953; however, in that year it fell on a Wednesday. Presumably, the set dresser used an old prop calendar for 1950 or 1939.
The sheriff drives John into the desert at night on instructions from 'Ellen' then after his meeting with an alien who tells him that they will be leaving Earth that night the sheriff drives John back to his house. All this action supposedly takes place at night but is obviously shot in daylight as there's strong shadows at john's house. As he approaches his front door which is under a porch and in shadow but in a close up of him he casts a shadow on the door.
When Putnam and Ellen land back at the airport in the helicopter, Putnam is holding his pipe in his mouth upside down (bowl facing down). Pipe smokers sometimes have the bowl upside down, especially when it's raining. They tamp the tobacco tightly, light it, and then turn it upside down to keep the rain out of the bowl. Some pipe smokers will have them inverted even when it's not raining, possibly as an affectation, or simply habit.
When the alien first goes walking about in the desert, the camera cuts to a startled owl, which tries to fly away only to be jerked back by the visible string tied to its leg.
The spider Putnam points out to the sheriff is evidently a toy tied to a string: it moves forward jerkily and without moving its legs.
The aliens take over the humans by enveloping them but when John goes into the depths of the mine where the spaceship is being repaired he finds an alien in his likeness yet he's never been enveloped.
John Putnam kneels and points out blood on a rock to Sheriff Warren. As he stands, he pushes on the rock and the rock indents.
When Richard Carlson and Barbara Rush blow out three candles, there's another half-second delay before the light in the room actually goes out. Clearly, the off-stage light, that was supposed to go out at the same time the candles were blown out, was turned off just a second too late.
The voice in off at the beginning of the film says it is early spring, but the calendar on the wall of the sheriff's office reads February 11, but in many parts of Arizona February is early spring.
When John, Ellen, and Pete return to the airfield in the helicopter, they have a brief conversation with rotor noise in the background; yet neither the main rotor shaft (behind them) nor the tail rotor are moving.
Just after the crash when the spacecraft door is opening you can see the silhouette of the stage hand pushing the door out of the way.
As the ship is coming toward the camera there is what appears to be a post and a mirror at the left side of the screen just before it hits. This may be part of the equipment needed for the 3D effect.
The opening of the film states that this is Sand Rock, Arizona. It is actually Victorville, California. All throughout the film there are Joshua Trees, which only exist in the Mohave Desert of California (where Victorville is).
If it were in fact Arizona, particularly Southern Arizona, there would be Saguaro cacti, which only exist in the Sonoran Desert (which is Southern Arizona & Norther Mexico).
When the aliens assume the forms of all the people they've kidnapped, they're always wearing the same clothes their victims had been wearing when they were taken - with two exceptions: Putnam and Ellen. In their cases, the aliens raided their homes and stole clothes for their "duplicates". First: how did the aliens end up in the same clothes worn by the other people? Did all these people have two identical sets of clothing lying around their houses? Second: why steal different clothing for the Ellen and Putnam clones? Third: at least in the case of Ellen, why did they empty out her entire wardrobe instead of taking just one dress? Fourth: if, under a different but unstated hypothesis, the aliens only appeared to be dressed the same as the others - i.e., through morphing or some other illusion - then why would they need to steal anybody's clothes?
All the selected body hijacked, taken over (attacked) citizens are first shown through alien 'bubble eye' Point of View and the human bodies then stashed away in the mine (scene at end), while they work on their ship: but the headline billed (Richard Carlson) character, sleuth professor, John Putnam never is: yet his 'body double' is the head alien fixing the spaceship ray ...
and like 'Ellen', is then wearing different clothes which is unlike all the other usurped citizen bodies in their same clothes.
When Ellen, wearing ordinary clothes, is taken over by aliens John goes into the desert on their instruction and she's wearing an evening dress.