The excellent Saw comes out on DVD this Tuesday. If you’ve got a cast-iron stomach, there is no better fictional exploration of the Prisoners’ Dilemma available. (If you don’t have a cast-iron stomach, may I suggest Pooh’s Heffalump Movie?)

The premise of Saw is straight out of intro micro: two men wake up chained in a room together, and soon learn that at most one gets out alive. And the execution is straight out of experimental economics: The characters’ first instinct is not to try to kill each other, but to cooperate.

But before long, we bump into a hard truth: Human beings are better than economic theory tells us, but also worse. Unselfish people might sacrifice their own interests to help others, but they also might sacrifice their own interests to hurt others. The characters in Saw start to accumulate grievance after grievance against each other, until the audience starts to wonder: Maybe these guys would kill each other even if they didn’t have to!

A lot of critics accused star Cary Elwes of “over-acting,” but I want to give him for the Oscar for Best Actor. Seriously. Elwes gives a restrained performance that credibly ramps up as the story unfolds. My jaw dropped at the end not because I couldn’t believe his character’s decision, but because I did.

Half the joy of Saw is wondering what’s going to happen next. But let me give you an Easter egg too cryptic to be called a spoiler: Apparently our serial killer is fairly familiar with the social science literature on life satisfaction!