It is a common misconception among fans that this is the first entry in the franchise to contain nudity. However, in the original film, a character named "Mark" is placed in a trap where his body has been covered in a flammable gel. While the scene is artificially sped-up, if you watch closely, he is actually completely nude, thus making this the second entry in the series to contain nudity.
Surprisingly, the film's most graphic scene - Jigsaw's wide-awake brain surgery scene - remained completely uncut by the MPAA. The filmmakers argued that it was no different from the kind of thing people could catch on any medical documentary on TV.
The nude actress being frozen to death - Debra McCabe - is wearing a mirkin (a wig for her pubic area) to preserve some degree of modesty. Ironically, this scene is very misleading as the set itself was extremely hot and the actress's breath had to be added in digitally.
1000 special posters were made and were sold for $20 each in support of Saw III and the American Red Cross. Tobin Bell donated 2 vials of his own blood to be dumped into the red ink vat. All 1000 posters were then printed with the red ink vat and later sold. However, the first print was put up for auction. It was also signed by the entire cast and crew. All proceeds from both sales went to the American Red Cross.
The script was being constantly added to during production. Leigh Whannell remained on set throughout filming so he could keep working on it. One climactic scene between Shawnee Smith and Bahar Soomekh was scribbled down on napkins only five minutes before it was shot.
Shawnee Smith mentioned in a commentary track on the Director's Cut DVD that she was certain she would receive an MTV "Best Fight" nomination for either her fight with Donnie Wahlberg or Bahar Soomekh, but neither made the nomination list. As it turned out the fight with Soomekh can only be seen in the Director's Cut.
Lionsgate wanted a vehicle for Bahar Soomekh after she scored a success with Crash (2004). Soomekh wavered over committing to Saw III (2006) as she was not a fan of horror movies. She claimed to have nightmares for the first month that she was on set.
According to director Darren Lynn Bousman, the fans of the "House of Jigsaw" message board heavily influenced this film. It is also dedicated to the memory of late SAW producer Gregg Hoffman after his sudden passing in December, prior to the release of Saw II (2005).
The DVD and Blu Ray case for Saw III lists Jeff's full name as "Jeff Reinhart." This name was never mentioned in the film, and was actually created by a fan from the House Of Jigsaw message boards who posted the name online. Director Darren Lynn Bousman later said that Jeff's full name is really "Jeff Denlon."
The trivia items below may give away important plot points.
Amanda (Shawnee Smith) was not originally supposed to grab Lynn (Bahar Soomekh) by the throat and threaten her in the sick room, as can be seen by her surprised facial expressions in the moments after. The line where Lynn says "you fucking freak" was not written in the script. Bahar added it in after Shawnee unexpectedly threw her against the wall.
Donnie Wahlberg went to great lengths to let on that he would not be appearing in the film, even to the extent of issuing a press release. This of course was just a smokescreen to make his appearance in Saw III (2006) all the more surprising.
Before settling on the final version of the Pig Vat, the creators and writers of Saw III (2006) went through a couple different versions of game. One of them had Judge Halden suspended above a meat grinder. As he was lowered down into it, Jeff would have to dive into a "soup" (probably referring to the ground up pigs that were instead poured onto the Judge) to retrieve the key. It was changed again until it resembled the final version, with the exception that Jeff wouldn't have to burn his son's possessions, but simply step down into the silo to free the judge. Leigh Whannell said on the commentary for Saw III (2006) that one of the reasons for the final change was that merely having Jeff dive into pig guts was more akin to something on Fear Factor (2001), and that by burning his son's possessions, it was more of an emotional conflict for Jeff than a physical one.
In addition to the appearance of Donnie Wahlberg, Leigh Whannell's cameo was also kept a secret. Whannell was uncredited and there was not publicity of any kind about his character Adam appearing in the film. The reverse trap of Amanda from the first film was reshot for the flashbacks and no old footage was reused.
Due to safety regulations, the prosthetics people can't entomb a person when taking a body cast. So, in order to create the frozen body of Danica, they made two separate casts of actress Debra McCabe, one of the front half of her body and one of the back half. The result was two separate pieces of the frozen body (one for shooting the front view of the body and one for the back).
Before settling on the final version of the Classroom Trap, the creators and writers of Saw III (2006) went through a couple different versions of the game. One of them had Troy suspended above the floor of the classroom by large meat hooks. They decided against this, as they figured it would be basically impossible to escape, and that it would be more thrilling if he was standing and able to rip the chains out. A second version had the hooks going through his eyelids, his fingernails, and his teeth. This accounts for two of the promotional posters for the film, one showing a mouth missing numerous teeth, and another showing three teeth dangling from wires.
According to producers Mark Burg and 'Oren Koules (I)', they had originally discussed having Kerry placed in a device that would pull her limbs in different directions, but instead thought of the ribcage trap.
Before settling on the final version of the Freezer Room, the creators and writers of Saw III (2006) went through a few different versions of the game, with only minor changes. Originally, the victim was going to be a male police officer, but they decided against it, instead going with the idea of a female witness. Instead of being completely naked, Danica was going to be in a T-shirt and panties, but they figured having her being sprayed would make the shirt stick to her body and become too sexual, so they decided to put her in the freezer naked instead.
The script and the deleted scenes verify that after their bloody conflict in the basement Amanda did not simply abandon Eric Matthews. Enraged from his insults she returned and killed him by stabbing him repeatedly. The producers mandated that Eric should not die and these scenes should be removed. The director strove for those scenes to appear in the final cut of the film, feeling that it would be a significant turning point for Amanda as she would start violating the rules imposed by Jigsaw. The producers however excised the death of Eric from the film in view to reinstating him in the upcoming 4th installment (which indeed happened). As it stands Eric's disposition is left ambiguous and the lines of Jigsaw explaining to Amanda that he cleaned up after her mess are left unresolved until the next film.
Before settling on the final version of the Rack, the creators and writers of Saw III (2006) went through a couple different versions of game. One of them had Timothy strapped down to a table that would fold on its hinges, bending his body with it and breaking his back. A similar idea had been brought up once before when thinking about Detective Steven Sing's trap. It was remodeled into the shape of a cross, but would still bend along hinges that would break Timothy's body until they decided they wanted the individual limbs being twisted instead.
Before settling on the final version of the Confrontation, the creators and writers of Saw III (2006) shot numerous different versions, all resulting in Jigsaw's death at the hands of Jeff. The only differences were the weapons of choice, among them the original circular saw blade that Jeff picked up before finding the high power saw. An alternate ending was also shot, using the concept of Lynn's "bomb" collar, which would detonate and shake the room following Jigsaw's death, knocking Jeff to the floor, unconscious. Upon awakening, Jeff would then find a tape, possibly the one Jigsaw played after his throat was slit in the given ending.
The surprise appearance of Detective Matthews was kept a secret until the premiere. Not only was Dohnie Walberg absent from every cast list, publicity still or press conference but all his scenes were scripted to appear at the end of the film during Amanda's flashbacks. The first scripted scene was Troy's trap. In the final cut however the bomb countdown is the second scene and the opening sequence is the successful escape of Eric from the bathroom. This at least establishes Eric's appearance in the film and eventually leads to the last scenes which reveal his fate.