20 Things You Didn't Know About Saw

While Leigh Whannell was writing the original script, he suffered migraines which were so intense, he worried he had a brain tumour. He was so paranoid, Whannell had himself scanned at the hospital.

After he received the all-clear, Whannell wondered how he would've reacted if he was told by the doctor that he had little time left to live. This helped him devise the character of Jigsaw; a terminally ill serial killer who forces his victims to face their own mortality.

Okay, Whannell had a premise... but there was one problem. He didn't have any money. Despite the fact Saw's budget was just over a million dollars, that was still light-years away from the money Whannell could spare. Whannell and Wan decided that most of the story had to take place in one place for budgetary reasons. Because of this, the pair strongly considered having the film take place inside an elevator. The killer would look at his prisoners through the lift's security cameras (which sounds like a fusion of Paranormal Activity and Devil).

In the end, the director and writer decided to shoot most of the movie in a bathroom.