"Knock" is a science fiction short story by American writer Fredric Brown.
It begins with a piece of Flash fiction based on the following passage by Thomas Bailey Aldrich: Imagine all human beings swept off the face of the earth, excepting one man.
[1]Fredric Brown condensed this text into "a sweet little action story that is only two sentences long".
[2] There have been three different radio adaptations (Dimension X, X Minus One and Sci Fi Channel's Seeing Ear Theatre).
There was a knock on the door ...The story won the 2012 Cordwainer Smith Rediscovery Award; James Nicoll, however, describes it as "fairly conventional".