MY friend KNS has written a cool piece on perpetual motion engines. The gist of it is that if a cat always lands on its feet, and a buttered bread always lands with the buttered face down, what would happen if u tie a buttered bread to a cat?
Reasoning is that the body comprising of the bread and cat would keep rotating unable to decide whether the feet lands first or the butter.

There is a simpler analogy though, what if u apply butter to both the faces of a slice of bread?
theoretically, you can see perpetual motion! In the first case, the cat is a living being, and may decide that it doesn't want to land on its feet at all and hence our engine goes for a toss. But the bread was a living thing when it was growing in some fields of Punjab in the form of wheat. Since then it has died many deaths and ceased to have a mind of its own. Therefore I am sure you can see a perpetual engine by just applying butter to both the faces.

Physicists studying thermodynamics, who have spent ages trying to prove that a thing called perpetual engine doesn't exist, please look at this and KNS's blog and change your way of thinking!!