Zen Koan.

In the film, "On the Beach" (1959), an American nuclear submarine is in Australia when an atomic war breaks out. A cloud of radioactive fallout is slowly covering the earth, moving south into the as-yet-unpolluted southern hemisphere. It will eventually kill everyone, everywhere.

The submarine sets sail to North America where a mysterious, intermittent radio transmission, random dots and dashes, has been detected. Hoping to find a living survivor in their own country, the submarine, protected by the ocean from the fallout, finally traces the signal to the US Pacific coast. They send a man ashore in a radiation suit to investigate.

He finds an unattended radio transmitter running off a generator, with a Morse code key tapped by a coke bottle attached to the drawstring of a rollup windowshade, bobbing up and down in the breeze. This is what has been tapping out the radio "message". There is no one there. There probably never was.

The meaningless dah-dits only spell out the sound of one hand clapping.