Deliberate mistake: In the final shot of the film, Jill's head moves slightly when she's supposed to be dead. In the commentary, Wes Craven confirmed this wasn't strictly intentional, but he decided to leave the take in on purpose in case he decided to bring her back in a future installment. But unless a sequel proves she's still alive, it's technically a mistake, albeit a deliberate one.
Factual error: Winter in Antarctica would not have a night and day as portrayed, with the amount of light changing so much during the course of 24 hours.
Plot hole: No one wonders what happened to all the staff and patients at that sanatorium? No police ever came there and checked the place out after 30 years? And all the patient records, furniture, etc are still there?
Factual error: When Nate dies by the alien moon rocks, his helmet visor "explodes." The visor in the film shatters like glass, but the real visors on actual spacesuits are made of polycarbonate, a plastic that does not shatter but deforms.
Plot hole: Everybody jumps into the water and emerges on the submarine except for Natalie. They're wondering where she is when they notice a flare. They realise it's her, and they send a search party. She's hiding on a bus maybe one to two kilometres away from the water. Her going there makes no plausible sense. Makes no sense how she held her breath underwater longer than anybody that they didn't see her and why she would go in the opposite direction of the sub. It was done to prolong the scene. (01:09:00 - 01:18:00)
Continuity mistake: During the bridge collapse scene, when Olivia is crawling on the beam, she is first seen on the part of the beam that is closer to Sam. Almost instantly afterwards, she is on the part of the them that is closer to Molly. The space between the two beams increases significantly between the two shots as well.
Factual error: The Song "Looking for the Magic" by the Dwight Twilley Band plays on repeat several times throughout the movie, however it comes up as track 1 on the CD player each time."Looking for the Magic" was never the first track on a Dwight Twilley CD - It was track 2 on the group's 'Twilley Don't Mind' album released in 1977. You can tell the disc is not a homemade mix CD by the printing on the top of the CD the first time it is placed in the tray.
Revealing mistake: While driving the Mercedes to the house of grandma, the gauges on the dashboard show speed is zero and the engine is cold.
Continuity mistake: When Valerie's father was the werewolf, his right paw was burnt. Then, when we see the hand later, there isn't a scratch on it, but again later, we see that it is, once again, looking burnt.
Visible crew/equipment: When Jack arrives with the shopping, a crew member in shorts is reflected on the glass. Clearly not Max.
Continuity mistake: When Justin gets a text from Mike's cell phone, it shows a close up of the screen. In the "to" box, it says Nikki although it's Mike's phone.
Continuity mistake: When Charley and Ed are arguing in the abandoned house, the light switches on the wall next to Ed change positions repeatedly between shots even though neither of the characters ever touch them.
Continuity mistake: When Lucy comes home at the beginning of the movie she quickly buttons the top of her dress. While eating dinner, it is open and then buttoned again between shots.
Plot hole: The very last scene shows Mary building a wall, apparently in her belfry. But there should still be the original wall that Rose built, with the hole in it that Mary smashed in. By killing Rose / having killed Rose, she prevents further harm, but all effects that took place before that (also the building of the wall), should stay (like her scars). It is very unlikely Mary broke down the whole wall just to add another body. (01:28:25)
Other mistake: In the hospital, Barrett had his right arm in a sling and his lower left leg in a cast. When the police/ detectives were trying to find Barrett, one detective said Barrett could not have driven himself somewhere because he had "a cast on his leg." The cast was on the left leg, so Barrett could have driven using his right leg, as usual. Maybe he couldn't have driven with a cast on his right arm, but the detective gave the wrong location of the leg cast. (00:50:30 - 01:13:45)
Continuity mistake: Three teen boys are abducted to be killed at the church. One breaks free and finds a weapons cache and dies in that room, while his killer dies outside that room. Soon after, the preacher and his wife find the dead church member, then look into the weapons room to see two of the teen boys dead, side by side. But the second hasn't been killed yet, and dies running away from the church later, shot by the the local sheriff by mistake. (00:40:40 - 00:48:00)
Suggested correction: The second boy, the one who got shot outside, was playing dead so the church members would leave him. It is not a mistake in the movie.
Continuity mistake: In the 'match' when he tags with John Cena, Fred is picked up by the rival vampire in a fireman's carry position (kinda like for Cena's Attitude Adjustment), but his head is over the opponent's right shoulder in the first, wide, shot and towards the left shoulder in close-up.
Visible crew/equipment: As Max opens the bathroom door on the plane, a reflection of the crew is visible in the door. (00:50:10)
Factual error: The tracks of the red-eyed horse in the snow are not tracks that could be made by a horse. A biped (a human) made the imprints in the snow.
Factual error: Mallory tells Florence that the school is in Cumbria. Cumbria didn't exist in 1921. It was created in 1974 from Cumberland, Westmorland and part of Lancashire.