Book excerpt: Freakonomics was a worldwide sensation, selling more than four million copies. Now Steven D. Levitt and Stephen J. Dubner return with SuperFreakonomics, and fans and newcomers alike will find that this freakquel is even bolder, funnier, and more surprising than the first. SuperFreakonomics challenges the way we think all over again, with such questions as: How is a street prostitute like a department-store Santa? What's the best way to catch a terrorist? What do hurricanes, heart attacks, and highway deaths have in common? Are people hardwired for altruism or selfishness? Can eating kangaroo save the planet? Levitt and Dubner mix smart thinking and great storytelling like no one else, whether investigating a solution to global warming or explaining why the price of oral sex has fallen so drastically.