在科幻爱好者中盛传的一则“世界上最短的科幻小说”是这样的：“地球上最后一个人坐在房间裡。这时响起了敲门声。”可以说，这比一个精确的定义更能概括科幻小说的特质。美国著名文学评论家伊哈布曾说：“科幻小说可能在哲学上是天真的，在道德上是简单的，在美学上是有些主观的，或粗糙的，但是就它最好的方面而言，它似乎触及了人类集体梦想的神经中枢，解放出我们人类这具机器中深藏的某些幻想。”
Knock (short story)
"Knock", written by Fredric Brown, is a science fiction short story that starts with a description of "a sweet little horror story that is only two sentences long." It then goes on to elaborate on those two sentences and build a more complete story around them.
It was published in the December 1948 issue of Thrilling Wonder Stories. There have been three different radio adaptations (Dimension X, Xminus One, and Sci Fi Channel's Seeing Ear Theatre).
Plot summary
The full story concerns Walter Phelan, the last man on Earth. The alien Zan have killed off all life other than pairs of specimens for their zoo of exotic Earth flora and fauna. Grace Evans, the last woman, is not overly impressed with Walter and maintains her distance.
The Zan, who are immortal, become disturbed when one by one the other animals begin to die. The Zan turn to Walter for advice. He tells them that the creatures perished from lack of affection and suggests that they pet the survivors regularly to keep them alive. He demonstrates with one of them. When the Zan begin dying, they depart the planet in fear. It is then revealed that the creature Walter advised them to pet was a poisonous snake.
Then Walter discusses the future of the human race with Grace. She is shocked by his proposal and leaves. The plot then ends with the two-line story:
- The last man on Earth sat alone in a room. There was a knock on the door...
