Saw

Saw [2004, directed by James Wan, starring Leigh Whannell, Cary Elwes, Danny Glover] [imdb]
Jay Kay: This Se7en look and feel alike tries an original approach to horror flicks, being shot over the course of only 18 days inside a converted warehouse. The slow beginning pulls you in inadvertedly for a pretty good scares along the way, ending in a action sequence with a twist.
Quote: John: Hello Amanda. I want to play a game. Here's what happens if you lose. The device you are wearing is hooked into your jaw. When the timer in the back goes off, your mouth will be ripped open. Watch. There is only one key to remove the device. It's in the stomach of your dead cell mate. Look around Amanda. Know that I'm not lying. Better hurry.