Continuity mistake: When Ariadne wakes in the Snow Fortress and the floor goes from under her, we can see her gloves fall in to the crack but in a different camera shot of her we can see the gloves are now back near her head again. (02:12:20)
Revealing mistake: After the sniper is shot he falls through the wall. Look at his silencer when he hits the ground - it bends where it attaches to the muzzle. A real metal silencer wouldn't do that. (00:41:25)
Revealing mistake: When the killer is attacking Cici on the balcony, you can see blood on Cici's back before she is even stabbed and both times she is stabbed, the knife that comes out of her back has no blood on it. (00:33:20)
Continuity mistake: When Corrine takes off her blouse, she shows her children seventeen scars on her back that she got from being whipped by the grandmother. Later in the movie, when Corrine is dancing at a party, she is wearing a strapless dress and there are no scars or any signs that she was struck with a whip.
Other mistake: When Nebbercracker is on the stretcher and is being wheeled away, the grass pulls off one of the last wheels. When the stretcher is loaded into the ambulance both of the back wheels are intact.
Factual error: In the cemetery, the skeleton of Gregory Peck's son is far too big to be that of a newborn, which it is supposed to be.
Factual error: When Holland March is swimming behind the bar with mermaids, "Get Down On It" from Kool and The gang is playing. That song did not come out until 1981 and the film is set in 1977. (00:39:50)
Revealing mistake: When Louis gives Gage the lethal injection, because the syringe is transparent you can actually see the prop needle retract in and out of the syringe as he supposedly injects Gage.
Factual error: Near the beginning of the film before James McAvoy heads up to the house for the evening meal, he is seen looking up through a skylight when a Lancaster bomber slowly flies overhead. At the time it was was supposed to be 1935. The Lancaster bomber did not fly until the beginning of 1941. Can't be an Avro Manchester either, they only had two engines and first flew in 1939.
Factual error: When the Ranger trainees first meet Samuel L. Jackson, he's wearing the rank of a Specialist on his collars even though he's a Master Sergeant. Title 18, Chapter 33 of the US code prevents the unauthorized wear of a military uniform (among other things), however this does not automatically correct the mistake since a common misconception is that one slight alteration is sufficient to make the uniform legal. Having the wrong rank on is too obvious of an alteration, especially for anybody who has spent more than a day in or around the Army and would still be punishable by law, if he was dressed in an attempt to fool your average citizen outside of a movie.
Visible crew/equipment: In a scene not too long after Tom Cruise attempts to revive a hooker who has OD'd, he is speaking with an older gentleman. The three are in a bathroom and the hooker is passed out on a chair. One of the shower or light fixtures toward the left of the screen is shiny, and in a shot during which the camera briefly tracks in reverse, you can see the camera, cameraman and the focus puller reflected. It's pretty clear and not all that fast.
Revealing mistake: In the library scene when Richie sees Pennywise the clown, all the balloons filled with blood are popping on people who aren't supposed to be able to see them, but one lands on a lady and you can see her jump as the balloon pops.
Continuity mistake: In the dormitory, when lovestruck Ron is going gaga over Romilda, he is wearing a brown sleeveless tee shirt and its tan trim has many holes. When Harry brings Ron to Slughorn, Ron is still wearing that tee shirt, but now some of the holes are gone and the rest of the holes have changed position. (01:26:50)
Continuity mistake: When Sister Irene's habit is ripped at the back, you can see a bra strap on her left shoulder which disappears when she is seen at the front and when the camera is closer to her back (when she has the pentagram carved into her).
Character mistake: The newspaper article states that Lucinda was thirty-three at the time of her death in 1988. However, that would make her just four years old when she wrote the time capsule note in 1959 - four years old in the 3rd grade?
Revealing mistake: When John Cusack is driving the actress, there is a shot looking over his right shoulder at the dashboard. The speedometer reads 0 mph. (00:08:15)
Continuity mistake: When Clouseau parks in front of the ministry of justice, he breaks the hood of two police cars. A few shots later, when we see him entering the building, only one of the cars is broken.
Factual error: When Bruce Willis is looking at his old high school news clippings you see a professional baseball score on one of the newspaper clippings. The game was Pittsburgh vs. Arizona Diamondbacks. The Diamondbacks were not a team yet when he was in high school. (00:33:35)
Continuity mistake: In the scene where Sophie finds the cross key behind the painting, her hand is holding the painting while the key falls, but in the next shot, her hand isn't touching the painting at all.
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.