Why Do You Hear Ocean Sounds In a Shell?

Seashells do not really make any sound of their own. Inside they have many hard curved surfaces, which are good reflectors for sound. So any sound waves that get inside are jumbled up by all kinds of echoes. When you hold the shell up to your ear, you hear the noise of all those jumbled-up echoes. That does sound much like the noise of ocean waves beating against a shore.