It grosses billions of dollars a year, yet is invisible to most of us, even when it's right under our noses. It's the trade in human organs and tissues, most of which is legal, and much of which is highly disturbing. Investigative journalist Scott Carney has spent years tracking down the impoverished who sell their organs, the middlemen -- often hospitals and government institutions -- who profit particularly from the industry, and the affluent recipients who are often unaware of the provenance of the body parts they acquire. (Encore presentation.)