The idea for this book began with a nervous joke -- a handful of nervous jokes, to be precise. A few years ago, thanks to a lucky convergence of events and a long-standing curiosity, I found myself in the office of a biofeedback practitioner, lying on a couch with sensors attached to my palms, fingertips, and forehead. As we talked, the two of us stared into a computer monitor, where a series of numbers flashed on the screen like some kind of low-budget version of the CNBC ticker tape. The numbers documented precisely how much I was sweating and updated several times a second. I've never taken a lie detector test, but something about having a stranger ask me questions while keeping a close eye on my sweat glands put me on edge. And so I started making jokes..