system
Given the following post, respond as if you're commenting on Reddit:
human
What actually causes cracking joints? Is there any real biological benefit?
gpt
Joints are two bones that are enclosed by a fibrous capsule.

The capsule itself is filled with a lubricant called synovial fluid. Synovial fluid contains gases that are dissolved in solution.

When we 'crack' our knuckles, for example, the joint capsule is stretched; but there's only a set volume of synovial fluid in the capsule. A putative mechanism for the 'cracking' sound is attributed to the sudden drop in pressure from the stretching of the capsule, leading to the dissolved gases to rapidly come out of solution.

Basically, it's a bubble popping in your joint space.

As for its whether its beneficial or detrimental, there's a lot of research out there and it's a topic of hot debate. IIRC it doesn't actually cause arthritis though.