Goodreads claims that the Washington Post has deemed the author, Mary Roach, to be "America's funniest science writer." As far as I know, that's accurate. Probably the funniest science writer in the world, unless there's some unexpected humor in Uttar Pradesh of which I'm unaware. Especially now since Jonathan P. Dowling has passed away.
Sometimes when reading "out there" pop-science books, I imagine the author commenting: Did I just blow your mind, reader? Here, I imagined Ms. Roach saying things like Did I just gross you out? or even Did you just toss your cookies? She doesn't shy away from the gross, the disgusting, the icky. It's science! (And sometimes, even better, quackery.)
As the name implies, it's a trip down your digestive tract, starting at the top, proceeding to the you-know-what. But she's the opposite of methodical; she talks about what interests her, and if you want a detailed discussion of intestinal villi or taste buds, you'll want to go to some more boring books. (They might be listed in this book's extensive bibliography, I haven't checked.)
So roughly, we have explorations of flavor sensing (diverting into the secrets of pet food); our arbitrary rules governing which animal organs/parts are just too nasty to consume; Fletcherism (chew your food, roughly forever). Perhaps more than you wanted to know about coprophagia (a highfalutin word about a lofalutin practice) in beast and man. Sometimes recycling advocates go too far.
If you eat something living, how long does it survive? Can it chew its way out? Can you eat yourself to death? What's the straight scoop on smuggling illicit items, er, down there? Fecal transplants, anyone?
And finally, Ms. Roach's discussion of Elvis's colon shows no reverence whatsoever to the King.
All presented with broad, wicked humor and (otherwise) fine, accessible writing. This book won't turn you into a gastroenterologist, but you'll have a good time.