There is much to enjoy about Mary Roach — her infectious awe for quirky science and its nerdy adherents, her one-liners, that giant snake hypothesis. She is beloved, and justifiably so. Which is why I feel churlish, and weirdly guilty, for not enjoying “Gulp” more. Take the frequent, and really quite juvenile, medical student gallows humor. She seems quite over the moon about a Frenchman whose stomach exploded as a result of a botched colonoscopy in 1977. For her this was an “internal Hindenburg scenario,” the colonoscope was “launched from the rectum like a torpedo.” Terrible deaths are scattered for amusement throughout the book. In Philadelphia’s Mütter Museum, Roach sees a photograph of a man soon to die from a hugely engorged colon. He reminds her of “the bastard offspring of Humpty Dumpty and Olive Oyl. . . . The cheesecake pose invites you to stare, but everything else says, Look away.” I don’t want to be a sourpuss for not finding it hilarious that sometimes people’s stomachs explode, but I can think of a third response alongside “stare” and “look away.” It’s “sympathize.” At such moments, “Gulp” is a bit too much like a highfalutin Ripley’s Believe It or Not! for my liking — a lot of digestive system trivia but not much heart.

But Roach did sideswipe me with an enthralling chapter on “the alimentary canal as criminal accomplice.” At a California prison she learns of an inmate who managed to get two boxes of staples, a pencil sharpener, sharpener blades and three jumbo binder rings up his “prison wallet” — jailhouse slang for rectum. His prison nickname became O.D., for Office Depot. She investigates how much damage a terrorist might do if he decided to swallow explosives — or have them surgically implanted — before getting on a plane (something Osama bin Laden apparently considered, according to documents found in his compound). The answer: almost no damage at all. Even a rectal bomb would do no more than blow the seat apart. All this is vintage Roach, as charmingly curious as the lab-nerds she eulogizes so affectionately.

But the main problem with “Gulp” is that in contrast with death and its aftermath — or sex, unfortunately, for many — we are already very closely acquainted with our digestive systems. There’s the disappointing sense that for every promised “unusual story” we get a lot of stuff we already know or will just find quite unremarkable. I don’t need to be told that the human tooth has an awesome ability to detect the tiniest grain of sand. It’s no surprise to learn that when we sense an assault by some alien invader, like vinegar, we instantly deploy our saliva foot soldiers to dilute and disempower the acid. We live with our saliva and our flatulence and our gastric juices every day. Especially gastric juices, in my case. I am a chronic reflux sufferer. It is forever bubbling upward when it should bubble downward. I ought to have torn through the chapters relating to stomach acids. But what do I get? Roach asks someone to dab some hydrochloric acid on her hand so she can “experience gastric acid.” Nothing much ­happens. After a few minutes there’s a mild itch, which then fades. Then we learn that mealworms don’t ­dissolve in the stomach because they’re protected by an exoskeleton. This is all perfectly fine, but doesn’t live long in the imagination.

And I really could have done without her opening chapter — a day at an olive oil tasting center. It’s so uneventful her usually enchanting asides feel strained to the breaking point: “I was right there with the numb-nose who wrote, on his answer form, ‘Oh, for a piece of good bread!’ ” she remarks. Her take-away, by the way, is: “Proficiency builds with exposure and practice.” On occasions like this I’m afraid I found myself wondering how many more pages until I reached the colon and the excrement.