Trivia: In Jigsaws lair, where he was caught, you can see items around the room from the house in which the 8 victims were being held. You can see the oar Amanda picks up from the basement and the X marks the spot photograph. These are clues to show that the camera footage is recorded. This is confirmed on the DVD commentary.
Trivia: The needle pit scene was done with real syringes. The crew had to replace the tips with fibre optic ones. The pit was filled with slime to make the syringes slide around more. 120,000 syringes were used during this scene. This from the DVD extras.
Trivia: During the beginning scene with Michael being tested you can see a close up of his eye and the knife very close. This was not actually filmed with the actor, it is one of the assistant camera men.
Trivia: During the opening scene Jigsaw shows the head-trap victim where the key is. Jigsaw is seen leaning over a table with the victim lying unconscious on it. This wasn't actually the actor who played Jigsaw; it was a cameo appearance from director Darren Lynn Bousman.
Trivia: When Jigsaw and Eric escape the lair via a hidden elevator, the low-budget of the film prevented the construction of an actual working elevator. Thus, some tricky photography and editing was implemented. For the first shot where we see Jigsaw and Eric "going down", the scene was simply shot by raising the camera vertically to give the impression of them "going down" on an elevator. For the next wide shot, simple digital effects were added to make it appear that the room was "lowering." And for the final shot, where we see the top of the elevator going down an elevator shaft, stock footage from the film "Hollow Man" was used.
Trivia: In the room with the razor blade box, if you look at the top of the frame, you can see a lock with a key in it. If the actress walked a few feet further, she could've unlocked the box and gotten the syringe. Obviously this would've defeated the purpose of her dying, but interesting to point out. Confirmed in DVD special features.
Trivia: During the scene where Detective Matthews is taking to Kerry in his office, you can see a mugshot of a man with an afro. This is the director Darren Lynn Bousman.
Trivia: The bathroom where Adam and Zep were found dead was a replica of the bathroom used in the first film. They re-created it from scratch by using movie stills from Saw 1. Confirmed on the Saw 2 DVD special features.