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. (00:17:50)
Continuity mistake: When Dorothy is letting Campbell live in her home, he picks up his bag and puts it on his shoulder. When he leans in to kiss her, there is no strap on his shoulder, then it's back again in the next shot.
Continuity mistake: Shelly stabs the killer in the leg with the scalpel. But when we see the killer following her, he seems unhurt and there is no blood or anything.
Revealing mistake: When Kate is on the phone complaining about the water being cut off, the iron overheats. Kate then runs over to it, and the shadow of a crewmember is cast on the iron and ironing board, then moves out of sight. (00:23:30)
Revealing mistake: When the Cherub grabs Ruthie and throws her into the shower glass panel, look very closely and the glass is all smashed before she even touches it. (01:09:15)
Deliberate mistake: Paige's stunt double being thrown into the hot tub is obvious. (01:14:25)
Factual error: Ruthie gets impaled on a jagged shard of glass from a modern shower door, but shower doors are made of safety glass (since 1977) - when they break they don't leave sharp knife-like shards, only tiny pieces.
Continuity mistake: Lily gets shot at the video show by the killer. The first arrow hits her stomach. In the close-up shot, the arrow is higher, just underneath her chest. (00:35:40)
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. (00:21:50 - 00:23:30)
Factual error: When Lily is being shot by the arrows, the first arrow just lands nicely in her chest, but when she falls out to the balcony after the second arrow is shot, they have gone all the way through her body.
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.
Revealing mistake: In the beginning of the movie when the medical examiner is about to perform the autopsy, if you look at the cadaver's stomach, you can clearly see that it is breathing.
Other mistake: When the cherub stabs all the body bags, he finds the one the girl is in then stabs her and blood drains down through the tube. That only happens when the body is on the draining table. Are we to think there was a hole in the bag? And even if there was, there's no way blood could have filled up the bag and drained out that fast.
Continuity mistake: When Paige is thrown in the hot tub by the Cherub, he pulls the cover over. Where did it come from? You don't see it before she is killed.
Plot hole: Why did the killer cut off the hot water? Did he think that Dorothy would come down and turn it back on herself with all those staff members in the house?
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.
Continuity mistake: When Adam gives Kate the lollipop as a gift, Kate writes "IOU TLC" on a laundry ticket. As she takes the ticket out her bag, there is the number "6443" printed in red on it. When she hands him the ticket though, the number is now "6335." (00:47:55)
Continuity mistake: When Paige is upstairs with that guy, she tells him to take off his pants and shirt and then she kisses him and places her hands on his chest, but when the camera angle changes just before she throws him on the bed, her hands are on his arms.
Continuity mistake: When the main girl gives David Boreanaz the note on the back of her dry cleaning ticket, she writes it very sloppily, but then towards the end of the movie when she finds Detective Vaugh's head in the pond with the same note next to it, it's written VERY neatly.
Continuity mistake: When Ruthie hits the killer with the pool stick, he has a long coat which goes down near his feet, but when he throws her through the shower and is trying to push her head down on the glass, he has a short coat which only goes down to his knees.
Answer: He doesn't kill her because she was the only nice one, whereas her friends( Paige, Lily, etc.) were all mean to him at the beginning.