How quickly can you find out what is unusual about this paragraph? It looks so ordinary that you would think that nothing was wrong with it at all and, in fact, nothing is. But it is unusual. Why? If you study it and think about it you may find out, but I am not going to assist you in any way. You must do it without coaching. No doubt, if you work at it, it will dawn on you. Who knows? Go to work and try your skill. Par is about half an hour.
(Puzzle by Kevin J. Lin)