When Donald Unger was a child, his mother and several aunts – and later his mother-in-law – told him that cracking his knuckles would lead to arthritis. Rather than stop (or at least do it less obtrusively), Unger embarked on his own experimental programme: for 50 years, he cracked the knuckles of his left hand at least twice a day, leaving his right-hand knuckles to crack spontaneously, or not at all. After 36,500 cracks or so, the results were clear, at least for Unger, who had become a doctor and published his findings in the journal Arthritis and Rheumatism. “There was no arthritis in either hand, and no apparent
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