system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do people hear that "ocean sound" when putting a shell to their ear?

Occasionally tried this when I was little, but never really thought about why this happens.
gpt
It's because of air bouncing around.  

Think about how you can hear the wind because it moves things around and even if there's nothing to move, you can hear it whistling past buildings or thumping into walls.  Well, even a tiny breeze makes noise but usually it's so quiet we can't hear it or don't notice.  That's where the shell comes in.  The shape of the shell magnifies the sound of a tiny breeze to the point where it's loud enough to hear.  So when you put your ear to a shell, you're not hearing the ocean, you're hearing tiny breezes moving in the shell.