Just how and why did Elvis Presley die on the toilet? What is a “prison wallet”? Which sex is the greater offender flatulence-wise? If these are the kinds of questions that consume you, you will gobble up Mary Roach’s “Gulp.” As with her earlier inquiries into dead bodies (“Stiff”), sex (“Bonk”), and outer space (“Packing for Mars”), Roach approaches her topic with robust curiosity and ready humor. Here she takes on digestion, broadly defined as everything that happens from the moment a diner sits down to a meal to the moment that diner, well, sits down again. Some of what Roach writes about breaches the boundaries of polite conversation — though she insists, “my aim is not to disgust” — but it’s also endlessly entertaining.
The story starts, somewhat surprisingly, with the nose, an underrated organ in the narrative of eating. But smell is where taste begins, Roach points out, and the sense plays a large role in the strange science of flavor consulting, as the author discovers when she auditions for a gig sniffing and rating various olive oils (she fails to make the cut). Roach is a fan of the field trip, visiting a pet food company (where she learns that dogs are very fond of the smell of cadavers and decomposing proteins in general), a laboratory studying saliva (where she follows spit-collecting instructions that include, “Gently chew the tampon for one minute”), and a professor in Minnesota whose entire academic career has been devoted to studying intestinal gas. She’s game to participate as well as observe, and finds the experts in these relatively lonely fields are usually quite eager to talk: “You get the sense oral processing experts are not, generally speaking, besieged by media inquiries.”