This question was posed to the Usenet Oracle:
 
 If you drop a buttered piece of bread, it will fall on the floor butter-side
 down. If a cat is dropped from a window or other high and towering place, it
 will land on its feet. But what if you attach a buttered piece of bread,
 butter-side up to a cat's back and toss them both out the window? Will the cat
 land on its feet? Or will the butter splat on the ground?
 
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 And in response, thus spake the Oracle:
 
 Even if you are too lazy to do the experiment yourself you should be able to
 deduce the obvious result. The laws of butterology demand that the butter must
 hit the ground, and the equally strict laws of feline aerodynamics demand that
 the cat cannot smash its furry back. If the combined construct were to land,
 nature would have no way to resolve this paradox. Therefore it simply does not
 fall.
 
 That's right you clever mortal (well, as clever as a mortal can get). You have
 discovered the secret of antigravity! A buttered cat will, when released,
 quickly move to a height where the forces of cat-twisting and butter repulsion
 are in equilibrium. This equilibrium point can be modified by scraping off
 some of the butter, providing lift, or removing some of the cat's limbs,
 allowing descent.
 
 Most of the civilized species of the Universe already use this principle to
 drive their ships while within a planetary system. The loud humming heard by
 most sighters of UFOs is, in fact, the purring of several hundred tabbies.
 
 The one obvious danger is, of course, if the cats manage to eat the bread off
 their backs they will instantly plummet. Of course the cats will land on their
 feet, but this usually doesn't do them much good, since right after they make
 their graceful landing several tons of red-hot starship and pissed off aliens
 crash on top of them.