This weekend, spectators will gather at a dozen Ripley’s Believe It or Not! Odditoriums across America to watch performers stick swords down their throats, through their esophageal sphincters and into their stomachs. According to the Sword Swallowers Association International, World Sword Swallower’s Day exists to celebrate the ancient art, dispel myths and “raise awareness of the contributions sword swallowers have made in the fields of science and medicine.”
If that last bit is a little hard to swallow, chew on this historical nugget: The first endoscopy of the upper gastrointestinal tract, or esophagoscopy, was performed on a sword swallower in 1868 by the German physician Adolph Kussmaul. After experiencing frustration at not being able to see far enough into the esophagus of a patient with a tumor, he was able to see all the way into the stomach of the sword swallower. The subject swallowed a 47-centimeter tube, which Kussmaul looked through using a laryngeal mirror and gasoline lamp.
Electrocardiography also owes a debt to the sword swallowing community, as the first electrocardiogram of the esophagus used a sword swallower as a test subject in 1906. The physician, M. Cremer, also a German, inserted an electrode into the sword swallower’s esophagus in order to record his heart activity.
The nineteenth and twentieth century medical contributions of sword swallowers are a fortuitous byproduct of the practice, which dates back to 2000 B.C.E. It began in ancient India, where it was performed, like firewalking, as a test of courage and a demonstration of faith. The practice gradually spread across Asia and Europe, morphing over the course of centuries from religious rite to street entertainment.
What was once a widespread global phenomenon is now a dwindling profession, with the SSAI estimating no more than a few dozen professional sword swallowers still performing. But those active in the small community will insist that people inclined to write them off as a circus sideshow acknowledge their contributions to the annals of medicine. So the next time a doctor looks inside your body through a tube, thank a sword swallower.
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Write to Eliza Berman at eliza.berman@time.com