Researchers pull fingers to solve why knuckles crack
Finding bursts bubble of popular theory
![Knuckles](https://i0.wp.com/www.sciencenews.org/wp-content/uploads/2015/04/ti_knuckle_free.jpg?fit=860%2C460&ssl=1)
KNUCKLING DOWN A knuckle at rest (left) pops when pulled. The sound of the knuckle cracking comes from a bubble (right, arrow) opening in the joint.
G.N. Kawchuk et al/PLOS ONE 2015 (CC BY 4.0)