The Gaps We Fill

For reasons unexplained, every person in the world is born with a large gaping hole in the centre of their chest. While not uncomfortable, it is widely considered unsightly and pretty much everyone tries to fill it with something. Some people with religion, and others just buy a whole bunch of stuff, and some even fill it with other people.
I left mine alone, though, because I discovered that if you run against the wind at just the right angle, it makes a lovely whistling noise.