system
Given the following post, respond as if you're commenting on Reddit:
human
Eli5: why does it feel good to crack your back?

I know what chiropractors would say but I want to hear others.
gpt
In people with back pain, one theory is that your joint is slightly off its axis, kind of like those sliding closet doors when one of the pegs comes out of the track.  Cracking your back restores the two surfaces of the joint to their optimal position.  

The "cracking" sound you hear is called cavitation, which is essentially gas bubbles forming and instantaneously being reabsorbed back into your joint fluid.  This happens because of changes in pressure in your joint.