Continuity mistake: At the start of the film when we see Pritchett shake hands with Blackburn, in this shot we can see that Eddie is standing in front of Blackburn and slightly to the side of him, yet in the following shot Eddie is nowhere to be seen, and the shot after he is back in front of Blackburn. (00:13:40)
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: 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 the guests are shown the guns in the casket, upon the first look inside they are not straight or in a perfect line, but in the close up shot they are straight. (00:28:50)
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: When Sara follows the imaginary Eddie into the room containing the big tank of blood, in one shot we see that Sara passes a glass medical cabinet, and in the following shot she is seen passing it again. (00:40:20)
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: 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: 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.
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.
Continuity mistake: In the scene where Evelyn and Steven are fighting, he has his hands around Evelyn's neck. Her hair is next to Steven's hand, then it is away from it. This changes from shot to shot.
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: 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.
Answer: The ghost that kills Melissa is the patient Vannacutt was dissecting. When Melissa initially sees them through her camera, what she's really seeing is the ghosts re-living their last moments.