Plot hole: When the Griswolds are at Wally World, supposedly the only people there are the guards. Who operates the rides for them?
Suggested correction: The guards also knew how to operate the rides.
Original mistake is correct. There were only 2 guards. 1 they kidnapped. The other they left lying like a dog until he could call the police. Therefore, there was nobody to operate the rides. Besides amusement parks don't train security to operate the rides.
Plot hole: At the end of the movie, when the water drains away, there would be no way for a) the amount of water to drain away that did and b) for the mammoths that came through to be completely dry. (01:16:20)
Plot hole: Wouldn't the bomb (when in the back of the truck of the bad guy driving away) vaporize him, considering he wasn't that much far apart than Allison was when she was tied up? He is even quoting as "Are you comfortable? Well it doesn't matter considering you'll be vaporized before you know it," when she was about 4 ft away.
Plot hole: When Marty lies on the conveyer belt on the way to the stone crusher he tries to wiggle off the belt. The little he seems to be able to move is not justified by the way his hands and feet are tied up. (01:08:30)
Plot hole: Goldie Hawn's character obviously has lost a large piece of her spine when being shot, as seen through the hole in her body. So how does she keep her upper body up straight? When Meryl Streeps character broke her neck she couldn't keep her head up, so why can Hawn walk around as normal?
Plot hole: When Melanie goes to meet Jake at the beach, it is pouring rain. Her hair is soaked and her dress is wet and muddy at the bottom. When they arrive at the wedding reception, her hair is much drier and her dress is perfectly dry and clean. (01:38:25 - 01:41:40)
Plot hole: Contrary to the realism of developing a video game Alex should have had external files such as character models, stage maps and coding on his laptop which he could have used as evidence that JP stole his game, It would be impossible to keep all of the games files on one disc especially if he wanted to change something in the game because if you want to modify a DVD-RW you have to erase the disc data and reburn it.
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: It's amazing that the two Chapman women weren't caught at "Rock for Daddy Day Care". One of them unzips a guy's dog costume in the middle of the path with everyone walking by. A little kid actually stares right at her when she does this. Also when Jenny puts the cockroaches in the salad, the people who were waiting in line for food would definitely have seen her. There are many more parts like this.
Suggested correction: And yet this kind of thing happens in real life too. Where somebody goes around causing a ruckus in a crowd, people around see them, but they say absolutely nothing and let them get away with it. It's called the "Bystander Effect," where people don't want trouble, so they assume somebody else around will do something. The encouragement of "See something, say something" comes from this exact thing. If it happens in real life, there's no reason it can't happen in the movie.
Plot hole: The psycho coed murders her lecherous professor (played by William Shatner) by pushing him out a window. In the very next scene, she's driving around with his body propped up in the passenger seat of her car. She weighed no more than 100 lbs., tops, and Shatner was easily at least 250 when this film was made. No way she could have dragged him to her car and lifted his dead weight into the seat, no matter how much adrenalin she was pumped with. Physically impossible.
Plot hole: It would have taken much longer to build the 54 acres of homes than the animals hibernated, so there's no way they couldn't have known what was going on around them.
Plot hole: How would Arnold know about the cop hitting the bus when he was running away from him during the parade? He was far past him at that point.
Plot hole: When Gwildor tells Julie and Kevin that he can use the Cosmic Key to take them to any point in time they wish, Kevin asks just for them to go straight home. As Kevin and Julie go through the portal, Julie turns around and shouts to Gwildor to send them back before being dragged through the portal completely. When Julie wakes up in bed, she discovers that Gwildor has sent her back to the day her parents were killed. Julie never said where in time she wanted to go, so there's no way Gwildor could know to send her back to the day her parents died.
Plot hole: Since "Dorothy Michaels" does not exist, she will not have a Social Security number. Even with her agent acting as a go-between, the television production company, her employers, would have to have this for their records. Supplying a false Social Security number is a very serious offense (and is instantly detectable), as is employing someone without one.
Plot hole: When the aliens kidnap the adults, the kids are left behind. But all the kids seen are around 11 and younger. Where are the teenagers or young adults? None of them are during the celebration scene nor in the arena on the alien planet.
Plot hole: At the end of the movie, when Lonette comes across Frank's dead body, she asks Nails what happened. Nails tells Lonette that he was pushed off a building by Holly Wood. Lonette then asks if Holly was in doodle form when she killed Frank. Nail says she was. There would be no way for Nails to know either of these things as he was trapped in the fountain pen when Frank died and wasn't released until the Spike Of Power was removed.
Plot hole: The main criminal puts on the "butt inspection gloves" whilst searching the first house, but when Alex sees him through the telescope he pulls down the blinds and has black gloves on. Returning outside, they revert back. However, how does Alex know the criminal donned the rubber gloves (when he describes him to his mother), if he saw what we saw through the telescope - the black gloves?
Plot hole: The movie is based in 1986 after the group time travels from 2010. That makes it a 24 year trip back in time. It is stated that Jacob is 20 years old. That is an error as this would make him roughly around 23 or 24 if he was conceived in 1986, which we saw near the end of the movie.
Suggested correction: This mistake has already been corrected. Cusack could have simply generalized his age when he mentioned it, probably not remembering his real age at the moment.