Revealing mistake: When Karen is searching the net, she is on "www.tdn_japan.con" [sic]. This address wouldn't work... Also the Google bar spells "Imaegs" not "Images." (00:59:30)
Revealing mistake: When the detectives were listening to the message on the answering machine, we heard it say the date was Thursday and states a time the message was left. When the camera shows the answering machine, you can see the display blinking between 1 (the current message) and CL (which indicates the time and date have not yet been set).
Revealing mistake: In the scene Where Karen is taking a shower and fingers show up on her head, she jumps and on the bottom left you can see she is wearing something red, and is not naked.
Answer: Because she was in love with him.