An Ass, having put on the Lion's skin, roamed about in the forest and amused himself by frightening all the foolish animals he met in his wanderings.  At last coming upon a Fox, he tried to frighten him also, but the Fox no sooner heard the sound of his voice than he exclaimed, "I might possibly have been frightened myself, if I had not heard your bray."

Moral: “Clothes may disguise a fool, but his words will give him away.”