Continuity mistake: In the scene right after Shelly's funeral when Kate and 'Adam' are talking by his car, he goes to kiss her when they are done. He tries to kiss her on the lips, but she moves to the side. At first he is kissing her on the left cheek and when the camera changes positions, he is kissing her on her right cheek.
Continuity mistake: In the scene when Kate is in the shower, in the opening shot, in her lounge the camera pans past a bookcase and into the bathroom. Kate then hears a noise, gets out the shower, and finds the water is cut off. When she uses the phone, halfway through her call, her iron overheats. The iron and ironing board are right beside the bookcase that the camera panned past in the opening shot. Trouble is, the iron and ironing board weren't by the bookcase in the opening shot.
Continuity mistake: When Paige is in the hot tube, minutes before her death, you can see the killer looking at her. There is a noise, and she looks back for a few short seconds but there has already been a rose placed there for her BEFORE she turns around to see what the noise is, she just doesn't notice it until she turns back around.
Continuity mistake: At the end, when the killer leaves Denise Richards a rose, you can see how badly the scene has been edited. If you watch closely you'll see that the rose appears from nothing - one moment there is nothing and the very next moment it is there, and it certainly doesn't look like someone's putting it, as it should be.