* DoingItForTheArt: All of the books in John Doe's apartment? They're ''all real.'' One of the special effects companies hired for the film spent two months ''hand-writing every single one of them''. Mostly by [[CrazyAwesome one guy]] who showed exceptional talent at writing journals like a crazy insane sociopath. He even included an authentic suicide note...
* DyeingForYourArt: [[spoiler: Creator/KevinSpacey]] shaved his head to play John Doe, on the condition that Creator/DavidFincher do so as well.
* ExecutiveMeddling: Somerset's Creator/ErnestHemingway quote at the end of the film was a sop to producers complaining about the film's extremely dark ending. Creator/DavidFincher's original plan was to have the film cut or fade to black immediately after Mills shoots Doe in the head.
* FollowTheLeader: Compare it with later ThemeSerialKiller flicks like ''Film/{{Resurrection}}''[[note]]A ''blatant'' rip-off starring Creator/ChristopherLambert and Creator/LelandOrser (who also played the man forced by John Doe at gunpoint to rape the Lust victim to death)[[/note]], ''Film/TakingLives'', ''Film/{{Anamorph}}'', ''Film/{{Horsemen}}'', ''WΔZ'', ''Film/SuspectZero'' or ''Franchise/{{Saw}}''. Of course that's not to say ''[=Se7en=]'' didn't borrow some elements from ''Film/TheSilenceOfTheLambs'' (and, for that matter, ''Film/TheAbominableDrPhibes''...).
* MethodActing:
** The actor who played the Sloth victim (Michael Reid [=MacKay=]) weighed 96 lbs. at his audition, and Creator/DavidFincher joked that he could have the part if he dropped another ten. Much to Fincher's surprise and horror, [=MacKay=] dropped six.
** The man who was forced by John Doe at gunpoint to rape the Lust victim to death is disturbed to the point of hyperventilating. The actor who played him, Creator/LelandOrser, sat himself in a corner, breathing very quickly in order to induce hyperventilation in himself to keep his performance authentic. He also stayed up for two straight nights before filming in order to seem believably exhausted and stressed out.
* PlayingAgainstType: Creator/RLeeErmey, the DrillSergeantNasty ''par excellence'', plays a mellow and soft-spoken police captain.
* RealLifeRelative: Creator/MorganFreeman's son Alfonso has a small cameo as the fingerprint technician.
* SerendipityWritesThePlot: Originally, New Line Cinema [[ExecutiveMeddling had no intention of using]] Andrew Kevin Walker's first draft the infamous DownerEnding originated, and Walker reluctantly went along with it. However, when contacting David Fincher, they actually sent him the wrong version of the script - i.e., Walker's original vision. which was faithfully adapted into the film itself. Fincher read it, loved it, and joined the production, and then refused to change the ending when the executives objected.
* ThrowItIn:
** Creator/BradPitt broke his arm filming the scene in which he chases John Doe. Although [[{{Irony}} the script required a (probably minor) injury]], the cast and such were written into the film.
** Mills' mispronounciation of the Creator/MarquisDeSade's name (see ItIsPronouncedTroPAY on the Film page) was an ad-lib by Creator/BradPitt. The first time he did it, Creator/MorganFreeman laughed out loud and said "Even Mills isn't that stupid!" Clearly, Creator/DavidFincher disagreed.
* WhatCouldHaveBeen:
** Andrew Kevin Walker wrote the screenplay with Creator/WilliamHurt as Somerset in mind. Creator/AlPacino was offered the role, but he was busy with ''City Hall''. Creator/GeneHackman turned it down because of the night shoots involved. Creator/HarrisonFord was also considered.
** Creator/DenzelWashington, Creator/KevinCostner, Creator/SylvesterStallone and Creator/NicolasCage were all considered to play David Mills (Washington refused the role, finding the content of the screenplay too disturbing, and specifically expressed regret at not accepting the role after attending a screening).
** Creator/RLeeErmey originally auditioned for the part of John Doe and [[Music/{{REM}} Michael Stipe]] was also considered for the role. Creator/ValKilmer was also offered the role, and he recommended [[spoiler: Creator/KevinSpacey]].
** An alternate ending revealed that [[spoiler:John Doe did not murder Mills' wife, only substituting a lookalike. Mills then has no justification for killing an unarmed man, and will spend the rest of his life in jail. Somerset decides not to retire, and instead gives his country house to Mills' wife and her unborn baby]]. Another alternate ending features [[BloodstainedGlassWindows a dramatic shootout in a burning, dilapidated church]] [[spoiler: in which Mills dies]], and yet ''another'' had [[spoiler: ''Somerset'' killing John Doe in order to save Mills from becoming "Wrath." In the finished film, the foreshadowing that Somerset will have to actually shoot his gun (or use his knife) is kept, but nothing comes out of it with the ending changed.]]
** When the movie was first pitched to execs, they had the screenwriter revise the film so it would be more marketable (happier ending, not as bleak etc.). But when they sent the script to Creator/DavidFincher, they accidentally sent him the original script instead of the revised one. Before they could correct their mistake, Fincher refused to make this film if the revised script was used.
** [[ArcNumber Seven]] years after the movie was released, there were plans for a sequel called (wait for it) ''[=Ei8ht=]'', telling the story of a psychic cop (Somerset) who developed a connection with the serial killer he was hunting. Creator/DavidFincher commented that he would rather have cigarettes put out in his eye than ruining ''[=Se7en=]'' with such a ridiculous sequel.
*** The sequel was eventually scrapped, but the idea evolved into the 2015 movie ''Film/{{Solace}}'' (starring Creator/AnthonyHopkins as the psychic).
* WrittenInInfirmity: After Creator/BradPitt severed a tendon in his hand, scenes were added to show why his character was wearing a cast.
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