Revealing mistake: Halfway through the movie, Alta is swimming in the pond, supposedly nude. However, when she climbs out, she can be seen wearing a flesh-covered swimsuit. (00:45:15)
Suggested correction: Alta never said she was naked. She didn't know what a bathing suit was and Adams assumed she was naked.
Factual error: At the end of the movie the cast is counting down to the explosion of the Krell furnaces. They reach zero and the furnaces explode. They see the light from the explosion just it happens. But they are 100 million miles out by then. The light would have taken over 8 minutes, about as long as light from the sun takes to reach earth, to reach the ship.
Continuity mistake: During the alien's assault on the ship, one crewman is seen near the spaceship's stairs firing a weapon. However, the weapon is pointed at a forty-five to sixty degree angle - at this angle, he would hit the bottom of the ship, not the alien that is much farther out.
Plot hole: Krell doorways and equipment suggest they are short, wide and 2-3 times larger than a human. Yet the shuttle pod the Commander, Doctor and Morbius ride in is designed for human size beings.
Plot hole: Morbius says no physical representation of the Krell remains. Yet later he shows the Commander a screen that contains the total sum of the Krell's scientific knowledge. So didn't the Krell study their own biology?
Other mistake: When the Id creature is melting through the door and Morbius is denying he subconsciously created it, the Commander draws his blaster giving the impression he will kill Morbius to save them if necessary. But Robby deactivated the blaster just a few scenes prior. Was he going to beat Morbius to death with it?
Suggested correction: That was a moment of desperation, so he wasn't thinking, and, well, yes anyway.
Continuity mistake: As Adams chews out the guards for allowing the alien onto the ship, he is fiddling with a pen. Cut to a closeup and the pen is on the table.
Visible crew/equipment: When the space visitors land on the planet and Robbie the Robot comes to meet them, you can see the reflection of a load of studio lights in the plastic visors of the vehicle Robbie is driving.
Factual error: The Doctor wonders how the creature can survive three billion electron volts. This is about 0.0000000006 joules. A baseball traveling a 2 miles per hour is one joule. It would take a lot more than three billion electron volts. It would take about 60 billion billion electron volts just to supply one joule. The energy hitting the monster was less than that supplied by running into a gnat.
Audio problem: When the crew are getting into the land rover tractor after the captain chews out his crew for letting the alien onboard, you can hear the "steel" door close with a heavy obvious metallic clang. A few seconds later the same door closes with a soft plywood thud, and a few seconds later it closes with no sound at all as if light as a feather. (00:36:00)
Revealing mistake: During the final scenes of the movie, Robbie the Robot is sitting at the navigator position. You can see his legs are a painted matte board and not his true legs. (01:36:10)
Revealing mistake: When Robby brings Doc Ostro in the Residence front room to lay him on the couch, you can see a number of the very thin black cables supporting the live actor playing Doc Ostro. Later, when Robby carries the 'body' out, it's quite obviously a mannequin due to the unnatural angle of the head. A dead person's head would sag against the robot's arm - this one is sticking straight out. The Robby suit was not only quite expensive for its day, but very noisy; requiring external power. As Robby is taking Doc Ostro's body out to the vehicle, Adams attempts to figure out the ID mystery. As he confronts Morbius, Robby walks back into the residence. If you look at his right leg, you can see the power cable trailing right behind.
Continuity mistake: When Robby is aiming the blaster at Adams, Morbius tells him to aim between the eyes. In the shot on Adams, the tip of the blaster can be seen rising at the edge of the screen, but Robby is too far away for that to be possible.
Character mistake: When Adams is chewing out Altaira for flirting with his crew, he says that he is "in command of 18 perfect physical specimens." With him, that would make for a total crew of 19 on the C57-D. But the complete cast only shows 18 names, including Walter Pidgeon as Morbius and Anne Francis as Alta. (And discounting Robby and his human handlers). Thus it would seem Adams is off by three. He has only 15 under his command. I've tried counting them when they're in group shots, but can't see everyone.
