Sometime before Mary Roach's new book got the title "Gulp," I like to think, that's what her editor did in mock, cartoonish panic on hearing that the author planned to dive into the human digestive system.

Letting this brilliantly mischievous writer, for whom no pun is ouch and no cow sacred, dip her pen into the font of all potty humor must have seemed even riskier than her previous excursions into corpses ("Stiff"), the afterlife ("Spook"), sex ("Bonk") and outer space ("Packing for Mars").

But dip she did - at one point she put her whole arm into a cow's belly - and came up with another quirkily informative pop-science entertainment in "Gulp: Adventures on the Alimentary Canal." For those so inclined, the wordplay is indeed joyfully awful.

The book has a simple structure: "Like a bite of something yummy, you will begin at one end and make your way to the other." Her guides, aside from her own tireless curiosity, are "scientists who tackle the questions no one else thinks - or has the courage - to ask."

"Could thorough chewing lower the national debt?" "Why don't suicide bombers smuggle bombs in their rectums?" Did constipation kill Elvis Presley?

Investigating how we taste things takes Roach to AFB International in suburban St. Louis, Mo., where pet kibble is coated with various flavors, and to the Olive Center in the Sensory Building at the Robert Mondavi Institute for Wine and Food Science on the campus of the University of California at Davis.

She visits "Food Valley," a collection of universities and research facilities in the Wageningen area of the Netherlands, where 15,000 scientists are "dedicated to improving or, depending on your sentiments about processed food, compromising the quality of our meals."

There, too, she finds the sunny saliva lab of Erika Silletti and pursues the question of whether spit works on food stains. She is referred first to a "chemist named Luis Spitz" and then to "a detergent industry consultant named Keith Grime."

A Michigan trapper's unhealing stomach wound allowed a doctor named William Beaumont to experiment ad nauseam with the man's digestive juices in the early 1800s. It was a strange relationship that Roach compares at one point to that of Wile E. Coyote and Road Runner, complete with BEEP, BEEP!

Shortly after an inevitable allusion to Monty Python's gluttonous diner and the fateful wafer-thin mint, we learn that "well over a thousand pounds of tobacco and hundreds of cell phones are rectally smuggled into California state prisons each year."

Let's pass discreetly over the anal violin and the product called Beano promoted with a windbreaker, and pause to marvel at the opening words of a chapter titled "Inflammable You: Fun With Hydrogen and Methane": "Long before anyone put a cautering wand up anyone else's patoot, the dangers of flammable bowel gas were well known."

Thence it's but a short distance to the room in Graceland where the King spent too much time on the throne. "Presley was given laxatives and enemas on an almost daily basis," according to his doctor, George Nichopoulos.

On the suicide bomber question: It reduces the potential damage. Excessive chewing and the national debt? Don't be silly, but Henry James, Franz Kafka and Sir Arthur Conan Doyle joined the fad.

As for her arm in the cow, "the fistulated - or 'holey,' as the students like to say - cow has been an ag-school standard for decades." Roach was doing a Beaumont, exploring the largest of the animal's four stomach compartments.

The roles are reversed somewhat as this many-course meal of a book winds down and Roach reveals: "I had my first colonoscopy without drugs." She waxes poetic about "laying eyes on my own ileocecal valve," then ends with the most perfect mix of tone and truth:

"You may be thinking, 'Wow, that Mary Roach has her head up her ass.' To which I say: Only briefly, and with the utmost respect."