system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can we HEAR our joints crack? How does sound escape the inside of our body?
gpt
The sound we hear is actually vibrating air that pushes against our eardrums, making them vibrate as well. But lots of things can vibrate (not just air), and when those things are in contact with air, they cause the air to vibrate as well. This is how materials can transmit or produce sound. For example, the sound of a violin is produced by the vibrations of its ~~snares~~ strings against the air. And the ~~snares~~ strings will also cause vibrations in the wood of the violin, which has a larger contact surface with the air, and thus amplifies the sound. 

Sound 'escapes' the body because it makes the tissues in the body vibrate, and then those vibrations reach the air. It's the same reason why inside a sealed (airtight) room you can still hear sounds produced outside: the sound is transmitted through the walls and (especially) the windows.