Saw (2004) -

The entire movie was filmed in just 18 days , with the central bathroom scenes taking only six days.

Many fans missed it on their first watch, but Jigsaw’s identity was actually revealed early on. In a flashback at the hospital, you can clearly see sitting on John Kramer’s desk. The Legacy of the Twist Saw (2004)

Because they couldn't afford a dummy for every scene, Tobin Bell (who played Jigsaw) actually lay on the floor in the middle of the bathroom for the entire shoot to save money. The "Hidden" Clue The entire movie was filmed in just 18