High-stakes lies have all sorts of consequences: perjurers are imprisoned and slanderers are sued. But when your coworker asks your opinion on his new haircut, a little lie feels obligatory. You lie much more than you’re probably aware of — but is that a bad thing?  Dessa finds out why lying can be a dangerous habit. She discovers whether polygraph machines really work, and why a professor of psychology rejoiced when a hidden camera caught his three-year-old son fibbing.  Deeply Human is a BBC World Service and American Public Media coproduction with iHeartMedia.