Like absentmindedly drumming on a tabletop, idly running a finger around the rim of a glass can make a kind of music—an otherworldly, ghostly music. How come?

Even if your family groans when you sing along to the car radio, even if you didn’t make the cut for the choir, and even if you got asked to be the drummer rather than the lead vocalist in your friends’ garage band, you sound exactly like your favorite pop (or opera) star in the shower. How come? And why do we enjoy singing in the shower to begin with?

There’s an official name for the horrible sounds that emanate from a blackboard: chalk squeal. Scientists say that the explanation involves both friction and resonance.

When you hold a large seashell to your ear, you can hear a distant roaring sound. It’s as if the great rumble and crash of the ocean waves is somehow trapped within the shell. So when you bring a seashell home from the beach, it keeps the memory of the sea alive.  But even if you don’t have a seashell handy, and it’s too cold to go to the beach, you can always hear the ocean. Just pick up an empty coffee mug, and hold it to your ear, tilted slightly away. Ah, there it is—the gentle, echoing roar of the waves.