Why do we always fall for surprise endings? It turns out that our capacity to be easily fooled in books and movies is made possible by a handful of predictable mental shortcuts. We talk this week with Vera Tobin, one of the world's first cognitive scientists to study plot twists. She says storytellers have been exploiting narrative twists and turns for millennia — and that studying these sleights of hand can give us a better understanding of the contours of the mind.