Continuity mistake: When Rachel is in the basement looking through the book and sees the newspaper article, if you pause the film when the article appears close up, you can read some of the article. This article has nothing to do with the title and photo caption above it, about the young girl in the bathtub, it appears to be about something political. The filmmakers assumed the article would flash by too fast for the viewer to read.
Continuity mistake: During the scene where Rachel puts Aidan into the bathtub at Max's house, he is wearing very light white boxer underwear as he is being put into the water. A little while later when Rachel pulls Aidan out of the bathwater, he is suddenly wearing very dark blue/navy colored boxers. Although water would darken the color somewhat, this is far too dramatic a change to be natural. The lighter color couldn't have possibly darkened to that extent. They are two different pairs of boxers.
Continuity mistake: When Rachel begins to brake her car after seeing the deer on the road, as the shots keep changing the markings on the road also keep changing. In overhead shots the markings are a single broken yellow line, but in closeups of the wheels, the markings are solid double yellow lines.
Continuity mistake: When Rachel pulls up to the old Morgan house she parks her vehicle on the gravel drive, angled into some tall grass. Yet when she leaves the house with the book, the vehicle is now parked halfway on the main road and is no longer angled (but is now much straighter) and is not facing any tall grass.
Continuity mistake: When Rachel is tucking Aidan into the bed at Max's house she puts a red blanket on him and then a brown blanket on top. Then during the next shots the red blanket goes from slightly visible to completely covered by the brown one and back again to being slightly visible.
Continuity mistake: In the first Ring it is revealed that Samara was in fact the Morgans' daughter. They showed her birth certificate with the Morgans as the parents and then the father before killing himself yells that his wife wasn't supposed to have a child. Yet a huge part of the second movie is about how Samara is adopted and Rachel talks to her real mother in an asylum. Um... What happened to what was found out in the first film?
Continuity mistake: After Aidan comes downstairs and sits at the table for dinner, he is flicking through his photography folder. In the shot when Rachel walks away from him and goes back to the oven, there is no plate at Aidan's placemat, yet it is there in every other shot before and after. His drink also moves without him touching it.