system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: what is happening inside our bodies when we hear 'cracks'?

My back cracks all the time!
gpt
If you're wondering how you can hear the noise, it's that your body is almost entirely water and sound travels very quickly and very efficiently through water compared to air. So you are hearing the crack through your own tissues. The water in your body is carrying the sound internally to your ears.