Lead is a metallic element that’s distributed across Earth’s crust. When it enters the human body, it can disrupt many critical processes that span various systems, producing a diverse set of symptoms. So, just how bad is lead for human health? And if it’s really that dangerous, how did it get into so many products? Gerald Markowitz and David Rosner dig into the lethal history of lead. Lesson by Gerald Markowitz and David Rosner, directed by Tim Rauch.