system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What actually happens when you crack knuckles and other joints.

Like, what actually makes them start cracking. Because for a long time I couldn't crack them, but at some point they just started cracking.

And does it lead to any actually bone/joint issues like people say it does?
gpt
I think the latest research explained it happening due to a kind-of vacuum being formed. 

The joints in your knuckles have a fluid between them, and when you stretch them to "crack" them, there isn't enough fluid to fill that gap. So you get a "vacuum", like pulling a suction cup off of a wall. This makes that "popping" sound.