I like to tell my students a story - it's about the martians, aliens, when they have been observing the earth for the last several thousand years from their very vast spaceships (we can't see, of course) and finally they go back home to report on their investigation of the earth and they say:
"Well, there are some reasonably somewhat intelligent creatures on that planet and, you know, they do things pretty much like we do, they have shelters and they have to find food, and breath oxygen and whatever. There is one really strange thing that they do: periodically they get together and vibrate the air..."
James Tenney
