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Why Knuckles Crack

Filed in Bizarre 4/16/15 at 9:54 am     1091     NPR

Scientists think they may have solved an old question about the cracking of knuckles: Why does it make that sound?

The crack apparently comes from a bubble forming in the fluid within the joint when the bones separate, according to a study published Wednesday. It’s like a tiny air bag inflating.

The findings confirm the original theory about knuckle-cracking, which was first proposed in 1947 but challenged in the 1970s.

According to Greg Kawchuk, a professor of rehabilitation medicine at the University of Alberta, that second group of scientists came along and said, ” ‘No, no, no — wait! We think what’s happening is, the gas bubble forms but then it subsequently collapses.That’s what makes the big sound.’ “

Read the rest at NPR