Continuity mistake: When the two girls are on the floor, just as the phone rings, Tomoko (the girl in green) has her right hand on Masami's (girl in red) shoulder. Cut to a different angle but now, Tomoko has her hand on Masami's arm instead of her shoulder.
Continuity mistake: When Reiko is talking to her camera man in the office, she places her left hand on top of her organizer. Cut to a different angle but now she has her left hand on the side of the organizer.
Continuity mistake: When Reiko picks up Tomoko's photos from the shop and is going through them, the way she's holding them changes subtly as it cuts back and forth from the over-the-shoulder shot to the low-angle-looking-up shot. (Most noticeably, in the over-the-shoulder shot, she has one photo pulled to the side but it's not pulled to the side in the low-angle shots).
Continuity mistake: During the funeral, Reiko goes outside and sees a condolence sign from Tomoko's school. In the first shot, she's not casting a shadow on it. The camera cuts to the opposite angle, and you can see for a second that she's suddenly partially casting a shadow on the edge of it. (Presumably because they adjusted the lighting in-between shots when they changed the camera angle).
Continuity mistake: When Yoichi is first introduced, he stands up from a chair. The camera cuts to the opposite angle, and suddenly his body has rotated about 90° towards his mom between cuts.
Continuity mistake: When Reiko is at her job at the beginning of the movie after interviewing the school-girls, the extras behind them are not consistent when it cuts from the wide to medium shot. Several of them are in different places and are doing different things.
Continuity mistake: When Reiko is introduced doing an interview with a schoolgirl, her cameraman suddenly moves back about a foot between shots after he tells the girl not to look at the camera, and they resume the interview. In the first shot, the lens of his camera is literally touching Reiko's shoulder... in the next, it's a good 12" behind her.
Continuity mistake: In the opening scene, there are two magnets on the refrigerator that look like cheese-wedges. They change positions twice during the scene. They rotate and move down about a half-inch at one point. Then, a few shots later, they are suddenly much closer together.
Continuity mistake: In the opening, there's a can of Planters peanuts on the table while Tomoko and Masami are talking about the cursed tape. When Tomoko gets off her chair and down on the floor, the can suddenly rotates about 45° from where it was a few shots prior. There's no indication that Masami touched it at all while it was briefly offscreen. (Best I can figure is that it might have gotten nudged between takes).
Answer: The other answer is not correct, although you could take it that way if you wanted. The novel upon which "Ring 0" is based was not even out at the time, nor was the prequel even planned at the time this movie came out. So that's not really the answer, although you could retroactively try to connect the two. As for the actual question: the crawling figures are typically viewed as being representations of the victims of the volcanic eruption that Shizuko (Sadako's mother) predicted. Especially as they appear right after words like "eruption" appear onscreen. Or they can be viewed somewhat more nebulously as representations of Sadako's pain, or the pain her victim's feel.
TedStixon