Revealing mistakes: In a close-up of Sadako in the end scene, one of her fake finger extensions is coming off.
Continuity: At the beginning of the movie, the TV in Tomoko's room is on. However, in the next scene when Tomoko has a close up, it's off. Neither Masami or Tomoko had switched it off.
Crew or equipment visible: Near the end, when the main characters lift the top of the well and shine the flashlight down inside, you can see the reflection of a stage-light in the water.
Factual errors: One the pictures received from photo shop there is a date, August 29, 1997. Later on the story tells "September 13, Monday". September 13, 1997 was Saturday.