This video has been making the rounds, I first saw it on Bruce Schneier’s blog, and it’s an absolutely amazing (though non-repeatable) solution to the Prisoner’s Dilemma as presented on a British game show:
That’s the game as originally stated, and it’s pretty much a textbook Prisoner’s Dilemma. What’s interesting about the clip is how the psychological trick used by Nick effectively breaks out of the normal rules of the game, so that it now looks like this:
By convincing Abraham that he absolutely would not Split, he presents Abraham with a much simpler choice – either Steal and be guaranteed nothing, or Split and at least have a chance that Nick would keep his word and Split the prize. That’s of course not a totally crazy idea – his nationally televised promise to split the money would at least provide some social pressure to keep the promise, and any non-zero chance that Nick isn’t lying would mean that Split is better than Steal for Abraham.
All in all, it’s a pretty brilliant trick, though it doesn’t really have the potential to work in the long term – once everyone’s seen it, then Abraham could be tempted to Steal and hope that Nick was counting on him to Split.