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?
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 civilised 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, that 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 very annoyed aliens crash on top of them.
Flaws In the Flying Cat Theory: A Response
A logical analysis of the BFAD (Buttered Feline Antigravity Drive) propulsion theory clearly demonstrates the impossibility of such a system.
Let us begin with a simple analysis.
Let us assume a normal Einsteinian universe (although a Euclidean universe would serve our purposes just as well, the Einsteinian is cheaper and drinks are readily available).
To test BFAD, one must procure:
Bread, butter (margarine, for some reason, will not work), a cat, a strapping device
Let us assume that all of these are readily available. Attach the strapping device to the cat.
See? No cat.
What has happened? We have run up against an a priori universal law. By a priori, we mean that it takes priority over either the Buttered Bread Principle or the Law of Feline Landings. What happens is that the instant a strapping device and a cat occupy the same four dimensional space, the cat disappears. Now, this can easily be tested, and has been repeatedly. There are two schools of thought about this phenomenon.
The first holds that a cat and a strapping device are constituted out of different fundamental building blocks. According to this theory, a cat is constituted primarily of superquarks, (called meows by current theorists). These superquarks demonstrate qualities that are both atomic (constituted as they are of groupings of normal quark particles) and feline (because these quarks exhibit characteristic of "charmed" or "lucky" particles). Again, according to this theory, strapping materials are fashioned out of non-charmed particles. Bringing the two together causes one or the other to cancel out. One aspect of this theory that has not been sufficiently explained to date is the fact that it is always the cat, not the strapping device, that disappears.
The second school of thought, and it is one that appears to be gaining ground in academic circles today, holds that cats are, in fact, super-intelligent pan-dimensional beings who exist in our four dimensional universe only because there is plenty of good food and a lot of creatures stupid enough to provide the food, along with plenty of attention. Whenever a strapping device appears, the cat simply opens a door to a different series of dimensions, and goes on an extended tour.
According to this theory, purring is a cat's way of maintaining a constant balance cycling across multiple dimensions. This school holds that antigravity is impossible, but that theoretically, a REALLY good grip on a cat, while reaching for a strapping device, could result in our ability to cross dimensions with ease (barring scratches, that is). Pessimists argue that if there was anything really interesting in those other dimensions, cats wouldn't spend so much time here, so why ask for a good scratching?