In the mid-1980s, a woman named Mariko Aoki sent a letter to Japan’s Hon no Zasshi, or Book Magazine, explaining a puzzling condition: whenever Aoki entered a bookstore, her bowels suddenly seemed to leap to life. The magazine printed the letter in its February 1985 issue, and it soon became clear that Aoki wasn’t alone. Other readers mailed in letters detailing similar experiences, and Hon no Zasshi capitalized on the momentum of the topic by publishing a lengthy feature article called “The Phenomenon Currently Shaking the Bookstore Industry!”

Decades later, a bookshop's mystifying ability to galvanize some people's gastrointestinal tracts into action isn’t exactly being taught in medical schools. While the condition hasn’t been scientifically proven, it’s garnered enough media coverage and public corroboration over the years to warrant a pretty extensive entry on Wikipedia. It’s called, as The A.V. Club reports, “Mariko Aoki phenomenon,” a fitting tribute to the woman who was gutsy enough to say what so many other bookstore browsers were thinking—and feeling. (Aoki reportedly doesn’t mind being the namesake.)

A handful of small studies conducted in Japan have suggested that the condition occurs all over the country, and it’s between two and four times more common in women than in men. People who work in bookstores might have built up an immunity to it, and few cases have been documented in children. That said, without research on a larger scale, it’s impossible to view these trends with any degree of certainty.

There’s a lack of evidence to support the theories that could explain Mariko Aoki phenomenon, too, though it’s still entertaining to ponder them. According to News Lagoon, one hypothesis is that the ink or paper used in the manufacturing of some books could contain a laxative agent, while another idea is that our societal habit of reading on the toilet has conditioned our bodies to induce a defecatory development whenever we open a book. It has also been suggested that all the bending and squatting we do while scanning shelves and pausing to read a few pages could move things along in our intestines. Yet another theory alleges we’re subconsciously overwhelmed by all the information we encounter in a bookstore, and the urge to empty our bowels is a psychosomatic attempt to escape all this data.

Next time you’re waiting in line at a bookstore bathroom, why not pass the time by discussing the merits of each theory with your fellow Mariko Aoki-sensitive patrons.