When you put a seashell up to your ear, what you hear is not the ocean. The sound comes from inside your own ear. The inner part of your ear, the part that is far back into your head, has both bone parts and soft tissue parts. In between these is your cochlea, which is a tiny organ that looks like a snail’s shell. Your cochlea is filled with fluid. This fluid helps you transmit sounds from your ear drum to your brain. And it sloshes around like waves. We don’t usually hear this sound because it is so quiet. But when you hold a seashell to your ear, this small sound echoes off the shell and back into your ear.