Other mistake: When Sarah Michelle Gellar is on the bus with her boyfriend, she sees Kayako face looking at her in the window reflection and panics. When she looks back at the window she sees the normal reflection of her face. Trouble is, her reflection is turning her head and looking side to side, whilst Gellar herself is looking straight and not moving her head at all.
Continuity mistake: When Karen goes into the cupboard upstairs, prior to meeting Toshio, she picks up a book. In one shot she picks it up by the page side, then when it cuts she is holding the spine side. (00:17:40)
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).
Visible crew/equipment: When Susan enters the building's stairwell, in the overhead shot you can see the reflection of the crew or equipment on the banister. It can't be Susan's reflection because she is relatively still, yet the reflection is moving and it is above where she could cast a reflection.
Continuity mistake: The message Susan leaves on the answering machine is a little bit different when Karen first hears it than when the detectives hear it again later in the movie, and when we actually see Susan leaving it.
Continuity mistake: When Yoko first talks to Emma, to the right of Emma is a striped blue shirt hanging over a lampshade. Between two shots, the position of the shirt hanging on the shade differs. (00:04:35)
Continuity mistake: When Karen and her boyfriend talk on her bed, and kiss, between shots Karen goes from having her head unsupported, to her head resting on her hand. (00:09:10)
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)
Continuity mistake: When Matthew arrives home at Emma's to find the place a dreadful mess, just before he walks over to Emma, who lays in her bed, the pieces of paper/rubbish that are around/near the pot of noodles, change and differ between shots. (00:31:55)
Continuity mistake: When Karen first goes to Emma's home, she opens the door, then the camera pans over wrappers and rubbish over the floor. Then it cuts to an overhead shot, and all the wrappers and rubbish have moved around and differed position majorly. (00:14:35)
Continuity mistake: When Yoko opens the door and ventures into the attic, the slide-door she pushes is nearly fully open. Yet when we see the shot of Yoko's legs dangling, the door is now much further shut. (00:06:20 - 00:07:35)
Continuity mistake: When Susan leaves her apartment when Matthew rings the bell, the door slams shut behind her. When she turns around to go back in, the door is open.
Continuity mistake: When Karen is on the ground towards the end, the gas container lid is on, but in the next shot the lid is off.
Audio problem: When Karen is in the house talking on the phone, she says "He won't come down," (referring to Toshio) but her lips don't move.
Continuity mistake: When Karen and Doug are walking down the street, right before talking about the Buddhist ritual, they are holding hands (right before turning a corner). In the next shot (right after turning the corner) they are not holding hands at all, and these two shots are supposed to be connected. (00:10:20)
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.
Audio problem: After the detective listens to the message that Susan leaves for her brother on the answering machine, the detective pushes the button to locate the missing phone. The detective as well as another officer begin to follow the sound of the ringing phone which is very loud and audible near them. As they begin walking down the hallway towards the door the ringing becomes muffled and when he opens the door it becomes loud again.
Answer: Kayako was murdered by her husband when he found out that she has romantic feelings for another man, since this would be a crime of passion driven by hatred the cutting out her face from all the photos then sinisterly pinning them to the door is another sign of his hatred. Like him removing her from the family and cause futher pain with the needles. Also to display her face would most likely be a way of shaming her further, insult to injury and all that.