In 2017, Matthew Williams, a thirtysomething software engineer with an athletic build and a bald head, went for a long bike ride in the hills of San Francisco. Afterward, at dinner with some friends, he ordered a hamburger, fries, and a milkshake. Midway through the meal, he felt so full that he had to ask someone to drive him home. That night, Williams awoke with a sharp pain in his abdomen that he worried was appendicitis. He went to a nearby emergency clinic, where doctors told him that he was probably constipated. They gave him some laxatives and sent him on his way.

A few hours later, Williams’s pain intensified. He vomited and felt as though his stomach might burst. A friend took him to a hospital, where a CT scan revealed cecal volvulus—a medical emergency in which part of the inte

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