In the August 9th, 1992 strip, Calvin wrote a Science Fiction Story that he shared with Hobbes. It was about an alien ship that came to Earth and stole all the water and air, dooming the people of Earth to extinction. Calvin thought it was too far-fetched, but Hobbes believed it wasn't far-fetched enough.
The aliens came from a far distant world
in a large yellow ship that blinked as it twirled.
It rounded the moon and entered our sky.
We knew they had come, but we didn't know why.
Bright the next morning, with noisy commotion,
the ship slowly moved out over the ocean.
It lowered a tube and drained the whole sea
for transport back home to their galaxy.
The tube then sucked up the clouds and the air,
causing no small amount of Earthling despair.
With nothing to breathe, we started to die.
"Help us! Please stop!" was the public outcry.
A hatch opened up and the aliens said,
"We're sorry to learn that you soon will be dead.
But though you may find this slightly macabre,
we prefer your extinction to the loss of our job."