Unlike the other Japanese horror remakes like The Ring (2002), Dark Water (2005), Pulse (2006), and One Missed Call (2008), this was the only film out of all the others that actually remained in Japan instead of moving the story to America.
On the DVD commentary, Sarah Michelle Gellar remembers that Jason Behr had previously guest-starred on her show Buffy the Vampire Slayer (1997-2003), but did not remember Clea Duvall, who also appeared in one story, "Out of Sight, Out of Mind," as a girl who turns invisible. This was because Gellar never had any scenes with Duvall's character while she was visible, so the actresses never actually met.
According to the DVD Commentaries and Featurettes, the house in The Grudge (2004) was built completely on a sound stage. It was based almost entirely on the house in Ju-on: The Grudge (2002). It was built like a normal house; the "house set" had two floors so that cuts did not have to be made when a character was walking upstairs. However, the attic was built separately from the house to allow for more room when filming.
According to the DVD commentary by the cast and crew, the first of appearance of the cat right when Karen picks up Kayako's journal was not, in fact, a real cat, but it was a fake cat held by a crew member, racing it in front of the camera.
While filming the infamous shower scene, Sarah Michelle Gellar discovered she was allergic to Japanese water, as it caused her skin to itch. So as to properly film the scene safely, Gellar was dressed in black hefty garbage bags from the waist down and in a little tube top.
Due to American violence ratings and the commitment to a PG-13 rating, the offscreen implication that Takeo repeatedly stabbed Kayako with a box cutter was omitted from the film (it was present in the original film). This is why she is covered in blood in the iconic staircase sequence.
The only film in the American remake trilogy that features Kayako covered in blood. In all subsequent films she is completely clean with no blood stains (although in The Grudge 3 (2009), Jake Kimble mentions that he saw her covered in blood).
Jason Behr met KaDee Strickland on the set of the film and both began dating due to their interest in Japanese culture (which is why they accepted their roles in the film) despite not sharing any scenes together in the film. They eventually married two years later.
The trivia items below may give away important plot points.
When Kayako is crawling down the stairs in the infamous staircase sequence, she is bending and contorting her body in ways that seem humanly impossible. Takako Fuji, being a trained contortionist and ballet dancer, performed the stunts herself. The effect was not a result of trick shots or digital manipulation.
There is a deleted scene after Toshio attacks Matthew, where Matthew becomes possessed by Takeo's ghost and kicks a visiting Susan out of the house. Director Takashi Shimizu cut it because it took focus off Kayako, despite being present in the original film.
In the original film, Rika (Megumi Okina) is actually killed by Takeo Saeki at the film's conclusion. Rika's American incarnation, Karen, instead manages to survive (though she later dies in the sequel). A remixed version of the original ending is re-introduced for The Grudge 2 (2006) involving Aubrey, Karen's sister.
Series Trademark: [bathtub death scene] Detective Nakagawa is lured by Toshio to an overflowing bathtub and attacked and drowned by Takeo. The following installments would feature Trish drowned by Toshio in The Grudge 2 (2006) and Brenda drowned by Kayako in The Grudge 3 (2009).
Yoko is killed when Kayako drags her into the attic and rips her jaw off, and then her possessed corpse kills Alex. This is a plot element that was not present in the original Ju-on: The Grudge (2002) film but was instead lifted from Ju-on: The Curse (2000), the straight to video film that preceded the former film.
The unrated version of the film reveals that Kayako got her revenge on her homicidal husband Takeo by ripping his jaw off then strangling him with her hair to death. Toshio's ghost then proceeds to swing his hanging corpse in the room causing the loud banging noises. Although this element was not present in the original Ju-on: The Grudge (2002) it was actually lifted from the original film's sequel, Ju-on: The Grudge 2 (2003).