system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: When your joints crack, what exactly is the pop sound you hear? Why do the pops sound different sometimes?
gpt
All joints have a capsule. The capsule contains the lubricant: synovial fluid. When the joint moves into end ranges, this allows bubbles to form within the capsule. The forceful pressure of the joint releases those gases resulting in a popping sound.