If a duck is standing on the edge of a cliff facing another cliff and yells, it will not echo.
If a duck quacks in the forest and there is nobody around to hear, it will not echo.
If you yell "Who put the overalls in Mrs. Murphy's chowder" to far-away ducks, the ducks will not respond, "We can't hear you, shout a little louder."
Behind the Legend
These silly bits of "trivia" are not only trivial but also untrue. Most likely the first (original) version is a folkloric muddling of two obvious facts: