The Ass in the Lion's Skin

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." Clothes may disguise a fool, but his words will give him away. - Aesop

[Courtesy of Aesopfables.com]