Chapter 5 of Slow Death deals with a naturally occurring toxin, the incredible element mercury. When I was a kid, my dad broke open a thermometer on a glass plate to show me how wondrous it is. We disturbed it with a pencil end, then watched it rejoin itself. Very cool. But he warned me to never touch the stuff with my bare hands. When I saw The Cove, I thought the most disturbing part wasn't dolphins being slaughtered, but the footage of the children affected by mercury poisoning. They looked a lot like the boy in this video...
