What Causes a Neck to Crack?
By C. CLAIBORNE RAY
The neck’s paired joints are filled with a bit of fluid, and when the neck is bent, a gas is released, creating that cracking sound, experts say.
Published: October 29, 2013 at 4:00AM
via NYT Science http://www.nytimes.com/2013/10/29/science/what-causes-a-neck-to-crack.html