* ActorInspiredElement: Meg was originally written to be helpless, but with Creator/JodieFoster's involvement, the character was revised to be stronger. The casting change also led to Meg's being rewritten to be similar to her daughter, whereas Meg had been different from her before
* CastTheRunnerUp: Creator/NicoleKidman was supposed to star, but wound up as the voice of Stephen's mistress when Meg calls.
* CreativeDifferences: Darius Khondji quit the production after several weeks as cinematographer to be replaced by Conrad W. Hall. Creator/DavidFincher later admitted that he micro-managed Khondji and didn't allow him to fully take part in the decision-making process.
* HideYourPregnancy: Creator/JodieFoster was already a few months pregnant when she started filming. The scene where she answers the door and talks to the cop was filmed last and they put a baggy sweater over her.
* NoStuntDouble: Creator/JaredLeto did his own stunts.
* TheOtherMarty: Originally Creator/NicoleKidman was cast in the lead role and shot a few scenes. She had injured her knee while filming ''Film/MoulinRouge'' and was replaced by Creator/JodieFoster. She did end up in the film as the voice of Foster's ex-husband's mistress when she calls him for help.
* ReleaseDateChange: The studio planned to release the film in February 2002, but it determined that production could not be completed by then.
* SeparatedAtBirthCasting: 12 year old Creator/KristenStewart looked like Creator/JodieFoster when she was that age and plays her daughter.
* VoiceOnlyCameo: Creator/NicoleKidman, who was originally supposed to play the lead, is the voice of Stephen Altman's mistress.
* WhatCouldHaveBeen:
** After Creator/NicoleKidman dropped out, Creator/SandraBullock, Creator/AngelinaJolie and Creator/RobinWright were considered to replace her.
** Creator/HaydenPanettiere was originally due to play Sarah. Unlike with TheOtherMarty above, she was replaced by Creator/KristenStewart without actually filming any scenes.
** Creator/DenzelWashington was considered for Burnham.
** Creator/MelGibson was originally considered for the part of the ex-husband, mainly for the PlayingAgainstType of him getting more and more abused as the film progresses.
** Originally Creator/DavidFincher planned to make the film in pitch darkness but this proved too impractical.
** Burnham was originally written to be "a slick, technical type" and the designer of the panic room in Meg and Sarah's home. Fincher did not think a designer could be persuaded to break into a home, so he rewrote the character to be a blue-collar worker who installs panic rooms for a living.
** Raoul was originally written to be "a giant scary hulking guy", but Fincher rewrote him to be "this wiry, mean kind of ex-con white trash guy". In one revised instance, Raoul punches Meg instead of slapping her to be reinforced as "an appalling character".
** A rather disturbing shot that was never filmed involved Raoul's mangled fingers being seen inside the panic room door, and falling out when it opened.
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