The Cat And The Birds
Cat heard that the Birds in an aviary were ailing. So he got himself up as a doctor, and, taking with him a set of the instruments proper to his profession, presented himself at the door, and inquired after the health of the Birds.
"We shall do very well," they replied, without letting him in, "when we've seen the last of you."
Moral: A villain may disguise himself, but he will not deceive the wise.