Revealing mistake: In the scene when the main character is in the library on the internet, she goes to a couple of websites. When the shot shows the URL up top, it is C:\windows98\mydocuments\etc.html. Instead of actually searching on the web they used a premade html page and accessed it from their computer. It's simple enough to just not display the address bar in your browser, so I don't know why they let this one slip through...
Visible crew/equipment: In the scene where Noah breaks into the mental institution's record room and is looking through Anna's files, there is a visible arm with a blue sleeve to his right, even though he is alone.
Continuity mistake: Samara, as seen in the psychiatric sessions on the videotape, has a prominent gap in her front teeth - yet when she decomposes in Rachel's arms down in the well, the skull that is left has perfect teeth with no visible gap.
Factual error: In the scene where Noah analyses the tape, he says that the 'timecode' seems to be invalid and says that every tape has a track where you can see what device was used to record it, etc. The video technology explanation originates from the original, Ringu, with the plot of The Ring changed to make it more applicable to average Americans. But a VHS tape does not have a special track for timecode. It is possible to lay a timecode onto the tape in either an analogue form via a special audio channel, or as digital information on lines 16 and 18 of the vertical interval. But this 'timecode' is only used for professional video editing. A standard VCR, like the one they were playing the tape on, does not use this, and therefore makes Noah's explanation a minute of utter nonsense.
Continuity mistake: After Noah is killed by Samara, Rachel comes in. She steps up to the chair Noah sits in, looking away from her. She rotates the chair counterclockwise to look at him. We don't see his face yet. We do see it near the end when Rachel has a flashback. For a split second, Noah's face is revealed in the chair now rotating clockwise. It should have been turning the other way around.
Continuity mistake: In the scene where Rachel bursts into Noah's apartment after he was killed, play it slow-motion when she flips the chair around. You can see up to half of his normal face & hair, with no decomposition visible, or hair loss.
Continuity mistake: In the extra/cut scenes included on the DVD, there is one where Rachel is in Katie's room snooping around. She goes over to the cabinet that has the TV on it and opens the top drawer, rummaging through it. After looking, she closes the BOTTOM drawer even though she was looking through the top one in the previous shot.
Revealing mistake: When Rachel is racing to save Noah, she is trying to call him on her cell phone. There is a shot of two hands on the steering wheel as the car turns and then a cut to her holding the phone in one hand a split second later while she was talking the entire time, showing that the shot with both hands was a stunt double and not her.
Revealing mistake: In the end, when we see the closeup of Samara's eye, you can see several white sheets used to reflect light into her face, as well as the reflection of the camera, in dead center of her pupil.
Continuity mistake: In the shot of the horse jumping off the ferry, the ferry's name "Quinault Seattle WA" is seen on its side. Rachel looks down at the horse in the water from the same place it jumped, but the appearance of the ferry's name is now different, namely the position of the two words "Seattle" and "Quinault" are now flush with each other when they were not before.
Factual error: The license plate on Rachel's car is not a valid Washington State license plate, while similar to the very outdated original issue plates, which would have never been issued on such a new car, they are missing tabs on the front which were mandatory on those plates and all Washington plates in 2002 when the movie was filmed.
Continuity mistake: Rachel goes to the lodge reception and the clerk points out the tape collection to her. She turns and is drawn to The Tape in the centre of the shelf. It is lying sloping up to the left, label spine outwards, spools on the left. When Rachel picks it up to drop it into her bag, it is spools to the right, label spine inwards.