Why do he hate broccoli? Why are we resentful of immigrants? Why does the smell of poo make us gag? In several new books and a steady stream of research papers, scientists have been exploring the evolution of disgust and its role in attitudes toward food, sexuality and even other people. This month, on Eureka, Umapagan Ampikaipakan speaks to Professor Val Curtis about the science of why we go "ewww".