Continuity mistake: In the end, when Michael has grabbed Karen's ankle and is trying to pull her down into the basement, Allyson grabs a knife off the floor and stabs him. However, if you watch very closely, you can see she's already holding the knife in one shot before she grabs it. (It's the shot right before Laurie screams "I've got you!" to Karen.) You have to pay attention because it goes by quickly, but you can see Allyson lifting the knife into frame for a split second, even though she doesn't pick it up off the floor until about 15 seconds later.
Visible crew/equipment: There is a shot of Holly crawling through a tight space with the camera facing her moving backwards as she crawls forwards (about 30 minutes into the film). In this shot, the wheel marks of the camera can be seen on the ground in front of her. (00:30:05)
Plot hole: When the cop shows Pam the newspaper clippings they include what look to be fresh photos of the real Jason from the events of Part IV, yet no photographer is ever seen taking pictures of Jason alive in the previous films and most likely wouldn't live long enough to publish the photo. (01:25:00)
Suggested correction: The picture was taken from security footage at the hospital after killing the 2 employees.
It was never shown.
Character mistake: Selena Gomez drives into town in a fully restored 1967 Pontiac Le Mans, which is a long box shaped car. However, when confronted with Bill Murray and Adam Driver, Adam Driver complements her on her 1968 Pontiac Le Mans, which is a completely redesigned shorter curved body style. The two look nothing alike.
Visible crew/equipment: When Freddy falls over the banister onto the stairs near the end, notice the crash mat he lands on. (01:18:55)
Plot hole: Peter goes into Carl's mind to save Catherine. When he's in there he sees the tank with the water nymph. On the tank are strange symbols which provide the FBI with the clue needed to find the latest victim. Makes sense so far. But, go back to the scene just after the FBI have captured the comatose killer and are looking in his basement. The FBI are looking at the contraption that the killer uses to suspend himself over the victim. On the contraption is the same symbol seen later on the water nymph's tank. Why didn't the FBI follow up the symbol then?
Visible crew/equipment: As the villagers are running away from Kong, when the mother rescues the young child, in the next shot look to the back right side of the screen. A member of this movie's production crew steps into the shot, stands there watching as the movie extras are running, and the shot cuts away. (01:17:29)
Continuity mistake: When Michael enters the Elrods' home and steals the knife, as he picks up the knife from where Mrs. Elrod had left it, there are several drops of blood that fall onto the lunchmeat, presumably from Michael's injuries from having been shot. A few seconds later when Mrs. Elrod walks back over to the lunchmeat and reaches for the knife and sees the blood, the droplet patterns are different.
Plot hole: When Bridgette ran through the glass and Linda and Jim were at the hospital Jim tells Linda he called her mom and told her what happened and she was coming to stay over the next day. Yet apparently her mom forgot what happened because she had her committed because Linda didn't remember what happened to Bridgette's face. Also, Bridgette was like 9. How come no-one just asked her what happened?
Revealing mistake: You can see wires in the scene where Regan levitates above her bed in the exorcism scene, lifting her up. The way they pull on her dress is also visible.
Continuity mistake: During the paper cut scene, when Bella is thrown against the table, there are 5 vases of flowers and 3 sets of candles. After she hits the table she lands against one of the vases and knocks the 2nd one to the floor, but the next shot shows only one vase left upright. (00:14:50)
Continuity mistake: When Hauser picks up the Admiral, after the Brain Bug attacks them, she has no yellow alien blood on her as she's being pulled up, but when the shot changes, as she's standing up, she now has blood on her face and uniform.
Factual error: The moon is full every night the highschoolers are at the lake house.
Continuity mistake: When the white boy is standing outside the car talking to the gangbanger inside the car, the gangster's sunglasses disappear depending on the camera angle.
Revealing mistake: When Henry's mom is pushed off the cliff her cable is visible.
Continuity mistake: When Christine is fixing herself after the guys smashed her up, her front end is shown to be perfectly straight for its entire width and the hood is missing. Near the end of the scene, the front end is shown crushed and unfolds again, and the hood appears from nowhere.
Other mistake: When the two Americans are walking on the moors, their shadows are always in front of them, despite them having changed direction numerous times. Additionally, with the moon always being behind them, how are their faces being lit?
Factual error: The type of surgery shown made by the machine transversely cuts the rectus abdominis muscles. Besides not being a standard surgical incision in order to "remove a foreign body" as stated, it seriously damages important muscles of the abdominal wall making any immediate active mobilization of the trunk virtually impossible, even under strong analgesia.
Continuity mistake: Rachel throws a couple of suitcases and Jamie throws 2 more and a sleeping bag down the stairs. Next shot shows a chair and boxes that were never thrown. (01:08:10)
Continuity mistake: When Gwen and the police are at the house containing the buried bodies of the victims while Finn and the Grabber are fighting, the Grabber's van is not in the carport. However, when Finn exits the house, and he and Gwen embrace, it is. (01:28:03 - 01:34:27)