Plot hole: In the first scene Alice hears on the radio that three teenagers had been murdered in Haddonfield just down the street from where they live. Yet a few scenes later, the sheriff finds out from his deputy that 3 bodies have been found. Wouldn't the police department know that before it made its way onto the radio news?
Plot hole: How did a woman who had just escaped from a mental institution get out of the country so fast? Even if she had a passport already, she wouldn't have it - the hospital or her family would. How could she get it back from them without SOMEONE turning her back in to the institution? It takes a lot to get involuntarily committed in the US, and I doubt she could get un-committed that fast, even with the guy she tried to kill vouching for her.
Plot hole: During the Congressional hearing, it is suggested that the alien signal could have been faked from a satellite - as Ellie only has her own experience to go on, it leaves her believing what happened, but still with an element of doubt. However, as a professional astronomer, Ellie would have immediately dismissed this since a simple parallax (triangulation) would have confirmed that source was at the distance of Vega - a distance far too great for any rocket to reach. (This is mentioned in the book). In fact, this is mentioned early in the film, when the employees in New Mexico calculate the source of the signal while it is transmitting prime numbers.
Plot hole: Sonny hides among the 1000 robots in the big store room. They are all placed in very straight rows. Sonny would not be able to take over another robot's place in the grid (when he starts running we see a large robot-sized gap) without getting another robot to move. And while Will Smith is running around the rows, he would have noticed if the others moved to make room.
Plot hole: After Nanahara and Noriko run away from Akamatsu at the school, Niida shows up from behind some bushes opposite the school and inadvertently kills Akamatsu with his crossbow. But Niida is Boy 16, which means he should still be in the school building (he's supposed to come out after Noriko, who's Girl 15). There's no way he has any time to get into those bushes.
Plot hole: When the police search the white car and the barn they fail to find the compartment in the car behind the boot in which the decoding equipment was hidden. This is completely improbable. It was a standard car, the compartment was not a secret add on, and the police were supposed to undertake a thorough search of everything.
Plot hole: Edward Lionheart severs the head of theater critic Horace Sprout while Sprout and his wife are asleep. (Lionheart gave them both a knockout injection). Sprout's wife (and his maid)discover the severed head in the morning, and both scream and faint. But in the next scene, critic Perry Devlin retrieves his morning newspaper and then reaches for his bottle of milk, only to find Sprout's head perched on the milk bottle. How did the head get from Sprout's house to Devlin's place?
Plot hole: In the scene after the bank job where Charlene waves Chris off alerting him of the setup, Chris drives away and is stopped by the cops to verify who he is. He has a fake ID and they let him go. The police CLEARLY know who Chris is and what he looks likes for most of the movie but somehow, those cops don't have anything with Chris' name and face on it?
Plot hole: In the middle of the film, after the custody hearing, Frank shows up at an event. Danny pretends that Frank dropped his wallet in order to have a brief conversation with his dad. Later, Rick confronts him about what they talked about. What does Rick expect? It's not like Danny will never be allowed to visit his father again. They are going to talk at some point. For Vince to expect that he will never talk to his father again is unrealistic.
Plot hole: At the start of the gun fight at the house, a snowball is thrown at Jack who then follows the person into the street. When they turn around the person is wearing a hockey mask and Jack realises he's in trouble. Jack would've seen the person wearing the hockey mask when the snowball was thrown, as the person had to be facing him to throw it. There was no reason after that for Jack to follow him.
Plot hole: In the scene where Lewis and Clark nearly hit the Event Horizon, One of the crew is calling out the closing distance and another confirms this information. Regardless of clouds obscuring their view they were aware of their proximity and the fact that they were speeding towards it and forced to attempt an abrupt stop makes no sense.
Plot hole: It is highly unlikely that the murderer knew Phil was going to put his ear to the stall when he heard the babbling. It is even more unlikely that the murderer is going to get him on the first stab through the stall. (Which also requires a lot of strength). We also have to assume that he spent time hanging out in the bathroom knowing Phil would go there to begin with, and that other two men with weak bladders were doing the same simultaneously forcing the victim to go to the stall to begin with. (00:07:45)
Plot hole: When Angel comes back to the doctor's home with food, he opens the bedroom door and turns on the light in that room. The lights are already on outside this room when we see him turn the doorknob. When Angel leaves, he leaves the light on in the bedroom and heads downstairs. Just before leaving out the front door, he turns off the light switch nearby. The shots changes to show the doc's body and the room going dark- as if Angel is still in the bedroom and turned off that light. (00:23:10)
Plot hole: When Eve is being led out to the airplane, she bolts when two shots are fired from inside the house (presumably Anna firing at Thornhill, not realizing that the gun was loaded with blanks). Moments later, she jumps into a car driven by Thornhill, and they escape together. There is no way Thornhill could have gotten there that fast, given that he was in the house only seconds earlier.
Plot hole: When the fog finally hits the lighthouse and is seeping in, the generator is hardly audible vs. how loud it was when it was first started.
Plot hole: When Margaret has to collect the $50,000, she goes around to various banks trying to get a loan on their house, which she can't get because her husband, co-owner of the house, isn't around. Why couldn't she just have taken the papers, said she was going to take them home to her husband, forged his signature, and brought them back? You can't exactly say she has either moral problems or isn't devious enough, since we've already seen her stuff a body into a dinghy, toss it into the lake, and come back to her house looking fairly normal.