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.
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.
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.
(at around 10 mins) On their way to the graveyard, Karen and Doug pass three schoolgirls on the street, a reference to Izumi and her friends, Chiharu and Miyuki, from the original Ju-on: The Grudge (2002).
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. Said scene where he drags her body across the house while holding a box cutter was restored in the unrated cut.
(at around 17 mins) 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.
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).
In just the first weekend alone, the film managed to gross $39.1 million in ticket sales (October 22 through 24, 2004), surpassing its budget. Ticket sales declined by the second weekend however by at least 43%, earning $21.8 million. Despite this, it was still a massive success and became the first horror film to top the Halloween box office since House on Haunted Hill (1999).
Detective Nakagawa is a composite character of sorts, as he shares the name and profession of Detective Kenichi Nakagawa from the original Ju-On: The Grudge (2002), but his personality and actions are closer to that of retired Detective Yuji Toyama, also from the original film. Like Toyama, he lost his colleagues to the curse, and also tries to burn the house down in this film.
Kayako's signature croak (also referred to as a death rattle), comes from the fact that her husband Takeo had snapped her neck but hadn't killed her, and she is trying to breathe through a broken windpipe. Her stumbles also come from the fact that her ankle broke as she was trying to run away from her husband. She's also covered in blood because he slashed her repeatedly with a boxcutter (the scene that implies this was cut from the film to receive a PG-13, it was restored in the Unrated Cut).
The trivia items below may give away important plot points.
(at around 1h 24 mins) 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.
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).
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 (2000), the straight to video film that preceded the former film.
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] (at around 1h 13 mins) 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).
SERIES TRADEMARK: [Ripped Off Jaw] Kayako kills Yoko by dragging her into the attic and ripping her jaw off. In The Grudge 2 (2006), deleted scenes reveal that the curse travelled to California and reached Karen and Aubrey's mother, and Kayako kills her by ripping off her jaw. Kayako kills Gretchen in The Grudge 3 (2009) by gouging her eyes out and ripping off her jaw.
A common criticism of this film, comparing it to the original, is the inclusion of the jawless Yoko scene as being an example of the filmmakers making the movie gorier than the original version for the sake of gratuity. This is despite the scene being a recreation of a scene from Ju-on (2000) in which the same thing happens to Kanna.
KaDee Strickland and Takako Fuji jokingly talk about Susan's death scene in the audio commentary as having lesbian undertones in it, because of Kayako hiding under the covers of Susan's bed before lunging out and killing her.
Yoko is a composite of 3 characters from the original films: Yuki and Kanna from Ju-on (2000), and Rika, the protagonist, from Ju-On: The Grudge (2002). Like Yuki, she is dragged into the house's attic by Kayako; like Kanna, her jaw is torn off; and like Rika (with whom she was originally going to share a name in the original script of this film), she is a social worker.
Peter Kirk, who Kayako had an obsessive crush on in this film, is an American incarnation of Shunsuke Kobayashi, a character from Ju-on (2000). Kobayashi was a college friend of Kayako and they reunited when it turned out that he was Toshio's school teacher, and she fell in love with him again and began writing about him in her journal. Takeo found the journal and in a fit of rage, killed Kayako and Toshio, under the deluded belief that Toshio wasn't his son. When Kobayashi investigates their home because of Toshio's repeated absences, he encounters their corpses and Kayako gives him a romantic kiss of death (in this film, Peter does the same thing as well but commits suicide at his home instead). During these events, Takeo had killed Kobayashi's wife and unborn child, and while carrying the dead fetus in a garbage bag in the city, Kayako emerged from a nearby dumpster and promptly killed him.
In the film, Karen finds Kayako's journal and curiously looks through it, coming upon a torn photo of Peter Kirk slotted inside. While it seems insignificant early on, the film later reveals that Kayako was in the background of the picture the whole time, heavily implying that she had stalker tendencies.
When Susan is in the taxi, if one looks closely at one of the adverts on the back of the front passenger seat, one will notice a staring eye printed on one of them. Later in the apartment, when Susan discovers Kayako under her covers, look closely at the wall. For a split second, you can see Susan's shadow and the shadow of Kayako, even though she isn't above the bedcovers.
Body Count: 9 - Doug, Matthew, Jennifer, Susan, Detective Nakagawa, Yoko, Peter, Emma, and Alex. Karen is the only main character to survive the events of the film. Peter is also the only character that wasn't killed by the curse, rather he committed suicide. The three ghosts in the film were long dead by the events of the film.