Revealing mistake: When the house has been locked down at the beginning of the film no moonlight could come in, however when the guests are being shown the coffin with the guns in there is a shaft of bright moonlight shining on to it.
Deliberate mistake: When Eddie and "Jennifer" are walking around the house alone, she is trying to tell Eddie that she's really Sara. But by the time she is explaining that, Eddie has disappeared. She doesn't find him until later. But from the moment she finds him (and he is talking to her) he calls her Sara, despite never actually hearing her say that. Also, after they all get back together, a few of the other people start calling her Sara as well, but no one actually heard that either.
Factual error: In the scene where the cast find the guns in the tiny coffins, they mention that it is not possible to tell if they are loaded because the clips are welded. Being semi-automatic pistols, simply pulling back the slide & ejecting the first round would have easily determined whether live or blank rounds had been loaded.
Continuity mistake: Right after Evelyn gets electroshocked, Blackburn takes off her mouth guard and a pool of blood leaks around her lips and down the side of her cheeks. In the next shot, there is a little bit on her lips, and a lot down the side of her cheeks, and several shots later she is seen with only a little dribble down her cheeks and none on her lips.
Factual error: Pretty precisely at 46:20, in the scene where Eddie and Sarah lost sight of each other down in the cellar, Sarah follows the apparition she thinks is Eddie. While doing so we see writing at a wall: "stehen nicht bei türen oder fenster wann dem Alarm gehört war" . The sentence contains so many mistakes that it's difficult to understand, but it roughly translates into "don't stand in doorways or windows after hearing the alarm". But it's a cellar, so there shouldn't be windows, and if the reason for the warning is the locking device: that closes only exits, and there are none of those in the cellar.
Continuity mistake: In the scene where Chris Kattan is sitting on the couch telling everyone that they are going to die and just before Eddie slaps the glass out of his hand, you see a back shot of Chris pouring the last of a bottle into a glass, then it cuts to the front and shows him pouring it again.
Visible crew/equipment: When Sarah and Eddie return to the saturation chamber after losing the other two, the camera shot is high up looking down into the room from a corner. In the upper right hand corner above the saturation chamber you can see the microphone fully in frame and "hovering" as they re-enter that room. It is also there a second time after the camera angle changes.
Deliberate mistake: In the scene about the Terror Incognita roller-coaster, when the rails break, they have ragged ends at the gap; after the first roller-coaster train derails, the rails move together again to close the gap and allow the second roller-coaster train to pass safely; but as you see the rails move together again, they now have neatly cut ends at the gap, not ragged ends. A deliberate error to mislead the audience, but an error nonetheless. (00:10:52)
Factual error: At the opening scene of the film when one of the insane people of the institute shoves pencils into the guys neck, the pencils we see are not long enough to go right through his neck. The insane patient would have to be holding the pencils inside the guys neck for them to go right through him. (00:04:40)
Continuity mistake: When Eddie and Sara are walking around in the basement, Eddie splits up from Sara, and then Sara spots him standing next to a doorway. In the first shot Sara walks around the corner and spots Eddie, yet in the following shot Sara is actually leaning against the doorway. (00:39:35)
Continuity mistake: At the start of the film when we first see Evelyn enter the house on haunted hill, she drops her briefcase at the door right on some kind of design on the floor, in the following shot the briefcase has moved forward some distance from where it was in the previous shot. (00:17:15)
Continuity mistake: When Sara and Eddie are in the saturation chamber thinking that Price killed Blackburn, they open the chamber and discover the body of Blackburn. When the body falls out the arms and legs face towards Sara, then when they look at it on the floor it is now facing the opposite direction. (01:08:50)
Continuity mistake: At the start of the film when Pritchett has led them all up to the house. In one shot we see Blackburn saying his line, "Wheres our host, the fabulous Mr Price?" look behind him at Pritchett he has his hand up to his glasses, then in the following shot he has his hand down by his side. (00:15:50)
Continuity mistake: If you watch the deleted scenes on the DVD, there's a scene where it shows the real Jennifer talking to the dead asylum owner about her getting the house in a will. When she walks in and screams and the camera goes to the guy it shows her walking in again.
Continuity mistake: When Eddie and Sara get back from the basement of the house, Sara is explaining what happened to Blackburn and Evelyn. In the shot of Evelyn, the bottle of Vodka on the top is only half full, if that, then when the camera returns to Evelyn the bottle is filled almost to the top. (00:42:00)
Continuity mistake: After Sarah sees glowing eyes Eddie for the first time, he walks off, and she follows him into a large room (looks like a morgue from the hatches in the wall). A POV shot shows the door to the room about halfway open. But, the next shot from in front of her, she steps through the door and it's wide open.