Continuity mistake: In the shot of the alien's tail wrapping around the back of Lambert's legs right before it kills her, the floor is different to what it was before, there is water suddenly falling from the ceiling when there wasn't before and her trousers have changed from white to blue. This is because that shot was originally intended to be used when Brett was killed.
Continuity mistake: When Annie and Laurie leave the hardware store to go to their babysitting jobs it is broad daylight. When they reach the houses apparently just a few blocks away, it is already dark.
Factual error: The idea that anyone survived living long term in Pripyat Hospital is absurd. At the time the film was set the hospital was still radioactive and prolonged exposure by living there would be fatal. Nobody could survive on the grounds for more than two or three months without receiving a lethal dose of radioactivity. Incidentally, prolonged exposure to radioactivity doesn't turn you into a deranged zombie - it turns you into a corpse.
Continuity mistake: When the Senator is about to be sacrificed, the cloth on her mouth immediately disappears for a split second. (01:29:35)
Character mistake: When Lisa is taken to the hospital, she tells Kathy that she saw the ghost of Jodie DeFeo. The name of both of the DeFeo's daughters wasn't Jodie. Their names were Dawn and Allison. Jodie was the name of a demonic pig that the Lutz's daughter Missy had befriended.
Suggested correction: While this is true in the original novel, the writers chose to change it to the DeFeo's daughter's name in the movie. Creative license doesn't count as a mistake.
Except that this is based on the real-life incident of the DeFeo family. This entry is not applied to the novel.
Factual error: This movie states that it is during the year 1973, yet in the beginning of the movie when they are driving in the van they are listening to "Sweet Home Alabama" by Lynyrd Skynyrd. This song was not released publicly until 1974. (00:03:10)
Revealing mistake: In the scene when the main character is in the library on the internet, she goes to a couple of websites. When the shot shows the URL up top, it is C:\windows98\mydocuments\etc.html. Instead of actually searching on the web they used a premade html page and accessed it from their computer.
Factual error: At the end when the shark is attacking the boat and the electronic device is used you can hear the shark roar. Sharks cannot produce this sound since they have no vocal cords.
Factual error: Federal institutions have strict rules for inmates or patients based on the reason for their incarceration, including substituting metal utensils with safer plastic ones. Despite being convicted of brutally killing his family, Myers is still trusted with a sharp metal fork - resulting in the nurse's death.
Continuity mistake: When Frost has the head pure-blood vampire on the beach, after he pulls out his first vampire tooth you see blood all over his mouth, but when it shows the close up of him pulling out the other tooth, there is no blood. (01:04:22)
Deliberate mistake: Leaven spends too much time thinking about if 645 and 372 are prime numbers to be believable. But she knows the factors of 649 and the result of 26 to the power of 3 almost immediately. Plus anyone with any maths knowledge whatsoever would know that any even number (or one divisible by 5) can't be prime, so 645 and 372 could be dismissed without even thinking about it.
Plot hole: When Andy turns into a werewolf, he kills both Amy and Detective Benbou. Later in the morgue, Amy tells him because of this that she is forced to become his "rotting sidekick." If this is completely true, then Detective Benbou should also be following Andy around but he isn't seen after Andy manages to escape from the morgue.
Continuity mistake: When Cheryl is running through the woods, she is wearing slippers that stay on up until she reaches the cabin door. However, in following shots, she is shown barefoot, and when Ash opens the door her foot is dirty as if she'd been running barefoot the whole time. (00:28:05 - 00:29:10)
Revealing mistake: Before Paxton is hit with the 3 prong instrument, you can see the bloody holes already on his shirt. (01:01:20)
Factual error: Towards the end of the movie, two characters finally make it to a Louisiana sheriff's office. The sign out front reads, "Vierge County." There are no counties in Louisiana, only parishes.
Factual error: No electricity, yet the washer is running.
Continuity mistake: About 10 minutes into the movie, when the truck is chasing the 2 college students in the car and starts ramming them, the bumper and the trunk is smashed in. The shot changes and shows the car's rear end and it is in perfect condition. This repeats at least 3 times.
Continuity mistake: Right after Bennett takes off in the plane, Claire throws a gun to Alice. Between the slow-motion shots, the gun switches position in mid-air before Alice catches it. In the shot of Claire throwing it, the barrel is facing to the right, meaning that it should be facing to the left in the shot of Alice catching it. But it still faces the right when she does. (00:58:30)
Revealing mistake: Right after Nell sends Hugh to hell, Dr. Marrow and Theo come out of hiding behind a pillar. As Marrow puts his hand on the pillar, it squishes in as if it was made of foam rubber, instead of stone. (01:39:50)
Factual error: When they go into the water, they put mouthpieces in, but, a few times, they talk to each other, which is impossible with mouthpieces in.
Suggested correction: Sorry to burst your bubble here but there is scuba equipment which allows for talking whilst using a regulator.
They're not wearing such equipment. In the movie they're just wearing regular mouthpieces.
In the DVD commentary the writers explain that the divers should have been wearing full face masks which allow for communication, but the director changed it for mouthpieces, but kept the talking in. They pointed out this mistake.