gribbles - Three Knocks

"When I talk about superstitions, this seems to make a great impression. Most of your audience - they've heard three knocks. Sure to be somebody in the audience who has. You hear the knocks, you see, and somebody goes to the door. There's nobody there. And sure enough, so the stories go, in the matter of a post or two comes a letter saying that somebody had died at exactly that time."