The script that was given to the new cast members of the "Saw" franchise was named "Evolution III". This was done so the script wouldn't leak out. Evolution Pictures is the company that owns Twisted Pictures.
Since the initial release of Saw (2004) on October 28 in 2004, every sequel since has been released the following year, one day previous to the release date of the year before it (e.g. Saw II (2005) was released on Oct 27th, 2005.)
The film was first locked on July 10, 2009. Due to the complex ending, the Producers and the studio took another week to perfectly calibrate the final 5 minutes. The film was then officially locked on July 21, 2009.
Director Kevin Greutert mentioned in the DVD/Blu-Ray commentary track that the twitching and shivering Amanda (Shawnee Smith) does in her scenes with Cecil (Billy Otis) was real due to low temperatures and rain in Toronto at the time of filming. Shawnee couldn't stop shivering because she was so cold and they were shooting outdoors.
The fish tank in William's (Peter Outerbridge) office was full of real piranha. When Jigsaw (Tobin Bell) notices them during his visit in William's office, he finds their appearance somewhat amusing. This may allude to the fact that piranha are predators, known for viciously preying on unsuspecting animals, and sometimes even on each other when food supply is low; from Jigsaw's point of view, a fitting metaphor for William's insurance company.
Less than a week before its premiere, the film was rated 'X' in Spain due to its "glorification of violence", therefore couldn't be shown in mainstream theaters, only in approved x-rated cinemas. Disney/Buena Vista then pulled the film from distribution, even though they already had a strong marketing campaign going on and over 300 copies of the film ready to be sent to theaters. Buena Vista tried to appeal the rating but was unsuccessful (this process took almost a year). In the end, they released the film in a cut version.
Prior to the film's release, Costas Mandylor (Hoffman) didn't even know if his character lived or died in the ending due to shooting multiple endings. One of those alternative endings included a revenge trap set up by Special Agent Straham for Hoffman to die in.
The extended driving scene with Amanda (Shawnee Smith) and Cecil (Billy Otis) seen in the Unrated Director's Cut was supposed to have a track from Smith & Pyle, Shawnee's country-rock band, playing over the radio but it was unable to be included in the final cut.
A week before filming began, director Kevin Greutert was informed that the film would be post-converted to 3D. Greutert was upset at this decision as he hadn't planned or storyboarded such a move. The idea was dropped for this installment due to time constraints but resurrected for the next film in the franchise.
The trivia items below may give away important plot points.
The first Saw film to not feature an audio tape playing in the final moments to explain one of the games. (Saws I, III, and IV ended with tapes from Jigsaw, II ended with a tape from Amanda, and V ended with a tape from Hoffman).
Amanda (Shawnee Smith) and Jill (Betsy Russell) can be seen mingling in the background during the conversation held between William (Peter Outerbridge) and John (Tobin Bell) at the party. Director Kevin Greutert stated in the DVD commentary that scenes involving Jill and Amanda greeting and talking to party guests were filmed but ended up getting cut in post-production. He also stated the party was intended to be a celebration of both Jill's pregnancy and the grand opening of her health clinic.
The hidden scene with Corbett (Niamh Wilson) and Amanda (Shawnee Smith) was originally supposed to have Corbett singing "You are My Sunshine" to herself with Amanda peeping through the peephole and singing with her to comfort the girl. The scene had to be changed because production was unable to get the rights to use the song. As a result, the audio of Corbett singing was taken out and it contains Amanda telling her not to trust Hoffman.
The sequence of the final scene with Detective Hoffman (Costas Mandylor) varies by version. In the director's cut the Reverse Bear Trap 2.0 timer gives a time limit of 60 seconds and is begun once Brent (Devon Bostick) pulls the "Live or Die" switch down. In the theatrical cut the trap is set at 45 seconds, a shorter time limit, and does not begin on Brent's cue. The timer is started after Brent pulls the "Live or Die" switch and Jill (Betsy Russell) pulls the trigger by closing the door.
The scene showing Amanda's involvement with the death of Gideon varies by version. In the director's cut Amanda's interactions with Cecil include more. She says "I've been good to you" and physically seduces Cecil into robbing Jill. In the theatrical cut the seduction and that line are not present.