This quick TED talk entry is courtesy of TED.com. Just like us, the monarch butterfly sometimes gets sick thanks to a nasty parasite. But biologist Jaap de Roode noticed something interesting about the butterflies he was studying â€” infected female butterflies would choose to lay their eggs on a specific kind of plant that helped their offspring avoid getting sick. How do they know to choose this plant? Think of it as â€œthe other butterfly effectâ€ â€” which could teach us to find new medicines for the treatment of human disease.