In the year 2744 a human survey team discovered a planet whose sole inhabitant was an enormous humanoid, three miles high and made of something very like granite. At first it was mistaken for an immense statue left by some vanished race of giants, for it squatted motionless on a vast rocky plain, exhibiting no outward sign of life. 

It had legs (two), but apparently never rose to walk on them. It had a mouth, but never ate or spoke. It had what appeared to be a perfectly functional brain, the size of a fifty-story condominium, but the organ lay dormant, electrochemical activity at a standstill. Yet it lived. 

This puzzled hell out of the scientists, who tried everything they could think of to elicit some sign of life from the behemoth–in vain. It just squatted, motionless and seemingly thoughtless, until one day a xenobiologist, frustrated beyond endurance, screamed, “How could evolution give legs, mouth and brain to a creature that doesn’t use them?”

It happened that he was the first one to ask a direct question in the thing’s presence. It rose with a thunderous rumble to its full height, scattering the clouds, pondered for a second, boomed, “It couldn’t,” and squatted down again.

“Migod,” exclaimed the xenobiologist. “Of course! It only stands to reason.”