There's this thought that if you want to know if someone is lying, you should be able to tell by just looking at them. We've been looking for physiological clues since the 19 twenties with the invention of the lie detector. In the past 20 years, estimateed, 200 thousand persons have staked their futures, many of them, their lives, on this machine. But what we're learning now is that a lot of those things they've been trying, simply don't work.