Plot hole: When the deputy arrives at the sheriff's house, Michael gets out and leaves the door open. The deputy comes out to the car and sees it open. And he thinks nothing of it, despite knowing he didn't open it. Logic would say, "Well someone else opened it."
Plot hole: Following Glen's death, Nancy tells her father to come across the street in 20 minutes to catch Freddy. She then goes to her house, checks and sets her alarm clock, and proceeds to rig the entire house with booby traps, including filling a light bulb with the contents of several shotgun shells, and has a heart-to-heart talk with her inebriated mom. When she gets back to her room to go to sleep, she checks her clock again. The time on the clock has advanced only ten minutes, not nearly long enough for everything she did.
Plot hole: George Lebay says that his brother died "6 weeks ago" inside Christine and that's why he's selling it. Later that evening after Arnie leaves his house and goes to Darnell's, Will Darnell says he "knew a guy who owned a car like that" and "the bastard killed himself in it." If it's only been 6 weeks since his death, shouldn't Darnell have recognized the car? It's not like there were lots of red Plymouth Furies (custom order color) running around the small town, let alone the USA, even in 1978. (Also considering how production even had a hard time finding them for the movie).
Suggested correction: He says he knew a guy with a car like that. It doesn't have to be the same colour or even the same generation. Just a Plymouth Fury.
Darnell basically said he knew THE brother of Lebay, not just some guy who owned a similar car. Darnell described Lebay's brother based on the story. Again, it was him, not just some other guy.
Plot hole: Not far into the movie, Starla decides to check out the basement to see what Grant's been up to. As soon as the door is opened she reels from the stench and we discover that it's full of rotting meat and dead animals. In reality, the whole house would have smelt like an abattoir for days before hand and the stench would have permeated out into the neighbourhood. A non-airtight wooden door would not have kept that kind of smell located to the basement only.
Plot hole: The police Inspector recounts the murders, comparing them to the ten Biblical plagues of Egypt, and he states that in keeping with this theme Dr. Kitaj was killed by rats. First, Dr Kitaj dies in a plane crash. Okay, he was attacked by rats in flight but nobody would know that - his plane crashes in a huge, violent fireball and nobody would find any rat remains after that. Second, there was no plague of rats in ancient Egypt! (Go ahead, look it up). Even if the police had made the connection between the mysterious deaths and the ancient plagues they would not make the connection here.
Plot hole: After his mother's death, Peter sets a camera up outside her therapist's office, so he can see who goes in and who comes out; he thinks his mother's killer might be one of the doctor's patients - a tall woman with long blonde hair. All he sees is people going in and people coming out, and then he sees her - the tall blonde. Problem: He never saw her going in, only going out, which is critical, because the killer is the therapist - a tall man - wearing a long blonde wig and make-up. Of course no-one says anything about "We never saw her going in, only out, so it must be the therapist!"
Plot hole: In the institute, Will's friend gets out of his room to get the guard's keys. He couldn't have gotten out of his room because there isn't a handle or door lock inside the room.
Plot hole: Sang-hwa forces a zombie inside a toilet stall. The zombie begins to bang on the door violently and Sang-hwa has to hold onto the door in order to stop the zombie from getting out. However, it is revealed later on that the zombies do not attempt to attack the humans or react violently or aggressively if they cannot see them. If this is the case, then this scene of the zombie banging on the door even when it cannot see any of the uninfected humans contradicts the rules that are established later on. (00:25:48)
Plot hole: Sergeant Howie is expected to report back to the mainland on the same day he left, and since he took a valuable aircraft with him on his trip it is inconceivable that his superior officers would not come looking for him if he didn't show up. First they would try contacting him on his radio and not receiving a reply they'd send out a search party, and they would do so within twenty four hours. Missing police officers are taken very, very seriously indeed.
Plot hole: It has already been mentioned that a certain shot reveals that Sidney isn't wearing the bullet-proof vest when she should be. Further to this, most of the shots in the climax sequence make it impossible for her to be wearing one, as you can see the contours of her chest throughout. A bullet-proof vest would flatten the appearance of this.
Plot hole: The aliens seems to be very strong, but not using technology at all. How come they defeated for example tank units? Doesn't look like they can penetrate steel with their arms.
Suggested correction: The aliens also demonstrate the ability to run extremely fast, easily able to outmaneuver a slow-moving tank. They would most likely jump on the top of the tank or rip the treads off, considering they still are extremely strong. They would also quickly jump onto a helicopter and take it down. As for other vehicles such as jets or aircraft carriers, the aliens either would have attacked military bases or taken the fight out to sea in ships. Whatever the answer, that particular element of the aliens is a large amount of possibilities, not a mistake.
If a waterfall can disorientate them, so would a jet engine or gunfire.
Something they teach in the military is the "ghost walk" - how to move silently. As the newspaper cuttings suggest, the noise angle was known about while there were still working printing presses, so it must have been a slow event. And a helicopter gunship can engage from up to 1km away, that's a long jump.
Yeah, how does the military never tried to use loud and/or high sound to defeat them once they found that they hunt using the sound? But to be fair they seem to be everywhere, so maybe they attacked in very large numbers.
That's actually clever (assuming the aliens didn't rip everything apart before coordinated strikes). Have some jets fly at low speed and A10s behind light up the space.
Plot hole: When the Grundel explodes near the end, Rowan looks out the window to see Uber Jason floating towards the rescue shuttle, only to be grabbed by Brodski who happens to fly sideways at a high rate of speed. Now provided it's feasible that Uber Jason can survive an immense explosion, how Brodski not only survived the explosion but managed to wind up away from the spaceship and far enough off to the right so as to catch Jason in mid-space is beyond me. (01:22:15)
Plot hole: It seems unlikely that Debbie would have managed to take the photographs of her husbands' murders she shows the Addams family at the end, especially considering the angle of the shot of the surgeon. He's not looking at the cam so she wasn't holding it.
Plot hole: Kazam is supposed to be a math genius, something that the plot hinges on, but he makes several mistakes when calculating the number of prime factors to find out whether a room is trapped or not. He says that 462 has three prime factors, when it has four, that 206 has four when it only has two and that 563 has two and 911 has three when both are actually prime numbers.
Plot hole: In the end, when Charlie is advancing on Emily while turning his light on and off, the final time he turns it on, Kathrine is in front of Emily. How could she get there so fast without being heard? There's at least 4-5 inches of water that would make sneaking very hard.
Plot hole: At the end, there is an explosion large enough to destroy and sink an entire ocean liner, but Julianna Margulies, who was sitting right next to where the explosion went off, not only lives, but is virtually unscathed? Yeah, right. (01:19:00 - 01:20:35)
Plot hole: The dead young girl who wears white has hemophilia (uncontrollable bleeding), and her mother states that she's scared of all sharp metal objects (scissors, etc.), yet she goes to play in an old abandoned steel mill all the time.