Claim: A duck's quack doesn't echo, and nobody knows why.
Analysis: You won't find this claim made in any scientific journal or textbook, please note. You will find it repeated in such questionable venues as email trivia lists, "true facts" Twitter feeds, and fruit drink bottle caps — reason enough to be skeptical.
The obvious logical question, the one neither asked nor answered by folks who tout this absurd factoid, is: why wouldn't a duck's quack echo? What could possibly be so unique about the sound a duck makes that it's exempted from the physical laws that apply to all other such sounds, e.g., a dog's bark, a cat's meow, a turkey's gobble, or a lamb's bleat?
The logical answer is: nothing.
For those for whom logic isn't enough, the claim that a duck's quack doesn't echo is empirically disproven by acoustical engineers here.
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Sources and further reading:
Fun Facts About Ducks
About.com: Birding/Wild Birds
Is It True that a Duck's Quack Doesn't Echo?
Ask the Experts, PhysLink.com
Is It True a Duck's Quack Won't Echo?
The Straight Dope by Cecil Adams, 22 May 1998
A Duck's Quack Doesn't Echo?
University of Salford: Accoustics, Audio and Video
Science 'Quacks' Urban Duck Myth
CNN, 9 September 2003
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