Trivia: When Officer Rigg is walking through the school, before he finds Morgan and Rex in the rod trap, he walks by a dark room blocked off with police-barrier-tape. Originally, there was a scene that revealed this was the room where Troy from "Saw III" died, but it was cut, presumably for pacing reasons.
Trivia: During the flashback scenes at the drug clinic, pay close attention. There are several characters from the previous films in a number of the shots. They include Paul (from the razor-room in the original "Saw"), Gus (who was killed by the gun-trap in "Saw II"), and the unnamed man who Amanda killed in the original film, among others.
Trivia: Donnie Wahlberg (who plays a major role in this film, as he has in the past two films) was not secure until 2 days before shooting began. It was suggested that his character be replaced by another character just in case, but director Darren Lynn Bousman persisted, and eventually secured Wahlberg.
Trivia: In each of the previous three films, the bathroom set had to be reconstructed from scratch when it was written into the script. (It was deconstructed each time under the assumption it would not be used again.) After "Saw III", the filmmakers decided not to totally destroy the set, as it might be used in future installments. And ironically, this was the first film in the series not to use the set, despite it being readily at hand.
Trivia: In the original script by Patrick Melton and Marcus Dunstan, Detective Eric Mathews (who had appeared in the two prior films) was set to be the lead character. However, actor Donnie Whalberg didn't originally want to return to the role of Mathews, and thus the script was re-written to center on SWAT team leader Rigg. Whelberg finally agreed to return as Detective Mathews shortly before filming began, thus leading to his smaller on-screen role in the film.
Trivia: When Rigg wakes up in his apartment after the games begin, and he is seen wandering through his hallway (as he is wandering past the hanging pictures), if you look closely, you can see a subtle grainy "haze" on and around his face, and notice that his face is somewhat brighter than the rest of his body. Because the scene is very dark, and Rigg's skin-tone is a very deep brown, his face was hard to make out in the scene, so his face had to be artificially brightened in post-production to be visible, resulting in the visible haze on and around his face.