When Dr. Steele, Nancy and Gen. Bowers fly off to Puerto Rico to search for Col. Frank Saunders/Frankenstein, they are seen leaving in a B-52 bomber; however, the plane they land in is a Boeing C-135.
When the Martians approach the pool party, it is daytime. The party itself is at night time.
Eight women are supposedly captured by the Martians, but when they are eventually released from their cage, nine women come out of it.
(at about 1:00 into the film) If you look at the inside of the Martians' purification chamber, you can see that it is made of plywood.
The MATS aircraft that Gen. Bowers and Dr. Steele use to travel to Puerto Rico in changes aircraft type and tail numbers in mid-air, or at least before they land in Puerto Rico.
When Mull the Space Monster is advancing during the end of the film, there is a brief shot of him from below where fluorescent lights may be seen in the ceiling. It is hard to believe that fluorescence would be present in a spaceship of Martian design.
In the film's close-ups of the Martians, the edges of the latex bald caps worn by the actors show clearly. The poorly concealed lines appear just above the eyebrows on the foreheads and reach down the sides of their faces to just below the earlobes. The pointed ears are also obvious make-up appliances.
At the scene in the film that shows NASA and the John F. Kennedy Space Center facade sign on the building, a circular pattern over the film's image can be seen. This is the result of shooting into sunlight and having the light hitting the front surface of the camera lens, where it bounces back to the back surface of the filter in the matte box.
When Dr. Adams (James Karen) asks the native storekeeper for a telephone, the man does not understand. Then he says "El telephone-o!" and hands the doctor a telephone that is not connected to anything. The doctor then makes a call.
At the beginning of the film, a Lincoln Continental is driving onto the base with three people in it, one driving and two in the back, and no blinds in the rear window. After this cutaway shot, however, there are then five people in the car, two in the front and three scrunched up together in the back, and blinds in the rear window.
Several times during the film, the actors' voices were dubbed in.
When the girl in the bikini is first captured on the beach by the Martians, her bikini is black, yet when she is shown on the Martian spaceship, it is a lighter color.
Princess Marcuzan, Dr. Nadir and their fellow Martians in the film repeatedly use military time when discussing time to begin operations, when they will arrive on Earth, etc. This terminology presumes that Mars is a planet with an orbit and a rotation identical to that of Earth. The likelihood of that happening is, quite literally, astronomically small.
Dr. Nadir tells Princess Marcuzan that the Earth's atmosphere will sustain them; however, all of the Martians wear their helmets both inside and outside the spaceship.
When Dr. Nadir is viewing his space scanner, he becomes alarmed that the Earthlings have launched a "missile attack" and it "may be aimed at us!". The next scene shows a rocket just igniting and barely off the ground.
After Col. Frank Saunders smiles and then freezes in place during his press conference, Dr. Steele later says he is coating the plug-ins in Saunders' head with silica gel to waterproof them; however, silica gel is a solid, supplied in the little disposable packages in many consumer goods that are made to absorb moisture from the air. For waterproofing plug and socket connections, they need to be coated with dielectric grease (which is often silicone-based).
Curiously, the Martians wear the same type of flight suits and helmets as the Earthlings.