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: When the security guards enter the cage housing the blown safe there are no traces of the water used to break the safe - not even on the (dry) floor. This happens only minutes after the explosion sent the safe door and gallons of water across the cage.
Plot hole: Klaatu is shot and his body is lying in a prison cell. Gort leaves the flying saucer and walks all the way to the heavily guarded police station in downtown Washington DC. Gort is 8 feet tall and is a robot plus he uses his noisy death ray to create a hole in the police station to retrieve Klaatu's body and nobody noticed him? On top of that, he walks all the way back to the saucer unseen with a dead body. (01:22:36)
Plot hole: When the "black diamond" is being turned into its dangerous form, the arms dealers get very excited. Yet all they actually see is a very pretty laser show. There is nothing to show that the object really has any destructive power. Arms dealers make their fortunes by being cautious and smart. They shouldn't be so quick to accept the claims of the bad guy and bid money on possibly useless stones. (01:18:20)
Plot hole: During the boxing match where Eddie Murphy is wearing the special contact lenses, he sees that Owen Wilson's life is in danger. So much so, that he rushes out of the ring instead of doing his usual grand-standing. But when he shows up at the tower to rescue Owen, he has on pants and a shirt. I guess he figured Owen could hold out long enough for him to get dressed?
Plot hole: At the end of the movie where David and his friends are attempting to break into Steve's house, David has the door code and attempts to gain access once by using it. Steve then tells his wife and the kids to go hide upstairs and turn off all the lights so nobody will know where they are. Then Steve and his wife go to another part of the house, away from the front door. Then, we hear David and his friends using axes and a big log to try and break down the door, "before* Steve secures the door with household appliances later on. Why wouldn't David have just kept trying the code?
Suggested correction: The reason David can not keep trying the code, is because the door has a lock on the top, and one at the bottom (middle regular lock). That middle lock is able to respond to the key/pass-code system, but the top one is not. In order to get in the house, David would have to be able to enter the pin (which, yes he knows) but with the top lock still locked from the inside he can not get in. I am assuming there is a key slot on the outside where he would need a key, and also I'm sure the family doesn't bother locking the top half of the door as no one else knows the pin (so they thought). And I'm guessing that they never locked it during the day either, and only at night.
Plot hole: When Rambo hijacks the Army truck, he throws out the driver, Robert A. and continues driving down the one-lane dirt road in the same direction. When Robert A. hits the ground, he immediately pops up and runs the opposite direction, away from where the truck is driving. A couple of shots later, we see a behind view of Robert A. running. It turns out that it is the driver's view from a Sheriff's vehicle. How could a car, especially a Sheriff's squad car, possibly come from that direction since it was a one-way road? And how could that same officer not see that the man driving the truck was Rambo?
Plot hole: James Bond shouldn't have gotten away at the end of the airport scene, where he steals an aeroplane and pretends to be a flying instructor. He had no wings with which to fly away, and he ended back up right outside the airport. So, the henchmen, who seemed to still be chasing him one shot before he parked, should have been right on him, waiting when he got out of the plane.
Plot hole: When Xander is driving onto the bridge, chased by the police cars, we see that there are police cars also blocking the end of the bridge to stop him getting away. How come none of them noticed the ruddy great ramp sitting alone in the middle of the bridge and moved it? It wouldn't take a genius to work out what he might do.
Plot hole: The assassin cuts a hole in the glass to kill the Federation president. But with the size of the hole and the placement of the scope on the phaser rifle, the assassin would not have been able to see out of the hole.
Plot hole: When Ripley goes to access the computer Mother, the entry door opens and closes with a hissing noise, a couple of minutes later you see Ash next to Ripley with a smile on his face. How did Ash manage to open the same door without it making the hissing sound? Ash could not have been in the room before Ripley came in - once Ripley has sat down at the console, it rotates on a 90 degree angle, this would have made it impossible for Ash to be hiding behind a desk or a computer console without being seen by Ripley. There are many doors on the ship that make the same hissing sound when the doors open, an obvious example is the infirmary door. And Ash couldn't have disabled the pneumatics of the door, because when Ripley exits the room, the hissing noise is heard again. (01:18:40 - 01:20:00)
Plot hole: Bond goes after Lupe after she leaves the casino table, and they have quite a lengthy, hush-hush conversation. It's a casino, and there are cameras everywhere. Certainly, this would have been brought to Sanchez's attention since he was already leery of Bond and possibly Lupe.
Plot hole: In the scene where Katrina is watching through Valek's eyes as he kills father Molina, Crow orders father Giteau to "find out where an old padre is missing". But Katrina never described father Molina, all she said was "He killed the priest". Crow could not have known the age of the man who was killed.
Plot hole: Slater decides to render the nuke inert by punching in the wrong code three times. However, when he does this, the nuke becomes armed, and Travolta reveals that he is one step ahead by having used a special kind of circuit board to produce this result. Two questions: One, once Slater has armed one nuke, why not arm them all? You've got nothing to lose, and you can keep Travolta from getting them for whatever evil purpose he has in mind. Slater plans to send them all to the bottom of the copper mine anyway, so just arm them all. Two, Travolta later arms a nuke himself, and then smashes the keypad with his gun. Well, if you can do that, why doesn't Slater just smash all the keypads as soon as he gets the nukes? Travolta would be defeated; movie over.
Plot hole: Calden would almost certainly not be allowed into the autopsy room without some protection: a facemask, goggles, gloves. Not only to protect from errant bodily fluids (as we saw) but also to protect from any infectious diseases those fluids (or any escaping gasses) might carry. Also, he runs the risk of contaminating the evidence.
Plot hole: When Jack The Ripper checks his watch before confronting H.G. Wells and demanding the key, the hands point to 8:50, the ensuing chase to the museum and demise of the Ripper may have used up a half hour or so, yet the time on the wall clock indicates that it is midnight.
Suggested correction: Movie time and real time don't match, so 3 hours has passed without all 3 hours being shown. The fact that the clock now shows midnight is meant to explain this fact without the need for subtitles to reveal the time.