Everybody eats, and we more or less know what that’s about. What happens after we eat – the transformation of food as it passes through our bodies – that’s more of a mystery, and a gross one at that. In her newest book, the science writer Mary Roach explores the interesting and kind of disgusting science and stories of our digestive tracts. Roach joins us on Tuesday to answer some age old alimentary questions: Why is crunchy food so appealing? How much food can you eat before your stomach bursts? And of course, did constipation kill Elvis?