Behold, the first-edition cover art for Fredric Brown's 1951 Space on My Hands. The classic science-fiction short-story collection contains "Knock," which begins with two of the most evocative sentences ever: "The last man on Earth sat alone in a room. There was a knock on the door ..."

Later editions of Space on My Hands featured another equally memorable cover image:

[Via Retrofuturism]