A chemical that kills the plants you don’t want—weeds—and keeps the plants you do—food!—seems kind of like magic. After all, weeds are the bane of farmers' lives, causing tens of billions of dollars in lost yield every year. So why is the world's largest herbicide company, Monsanto, so unpopular that it's been referred to as MonSatan? How harmful are today's herbicides for us humans, and for the environments they're seeping into? And do we need weedkillers to feed the world? In part two of our three-part series on weeds, we take on the big questions around this “bad seed” of the farming world—and the fascinating story behind the scrappy St. Louis startup that hooked the world on herbicides.