When we see Kayako crawling down the staircase towards the end in the infamous staircase sequence, she is contorting and bending her body and limbs in ways that seem humanly impossible. Takako Fuji, being a trained contortionist and ballet dancer, performed the stunts herself; the effect is not a result of a trick shot or digital manipulation.
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.
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.
In the original film of which this is a remake of, it featured a subplot involving three schoolgirls encountering the curse. Although it was omitted from the remake, it was restored in the film's sequel, The Grudge 2 (2006).
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).
The trivia items below may give away important plot points.
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).