Take a listen to this recording of a shaking matchbox with headphones:

Creepy, huh? The three dimensional effect comes from the filmmaker using a binaural dummy head to record it.

This fake head has a microphone in each ear, so the sounds get reflected through the dummy ears just as they would in nature. Listening back on headphones creates the illusion that these sounds are located in the 3D space around your head.

I bet you thought the wrinkles in your ear were just for looks, right? Actually, they’ve evolved that way to do two important things for you: