Now and then, teaching may approach poetry, and now and then it?may approach profanity. May I tell you a little story about the great?Einstein? I listened once to Einstein as he talked to a group of?physicists in a party. "Why have all the electrons the same charge?" said he. "Well, why are all the little balls in the goat dung of the same size?"?Why did Einstein say such things? Just to make some snobs to raise?their eyebrows? He was not disinclined to do so, I think. Yet,?probably, it went deeper. I do not think that the overheard remark of?Einstein was quite casual. At any rate, I learnt something from it:?Abstractions are important; use all means to make them more tangible.?Nothing is too good or too bad, too poetical or too trivial to clarify your?abstractions. As Montaigne put it: The truth is such a great thing that?we should not disdain any means that could lead to it. Therefore, if the spirit moves you to be a little poetical, or a little profane, in your class,?do not have the wrong kind of inhibition." - George Polya's Mathematical Discovery, Volume 11, pp 102, 1962.