Lots of people seem to think a duck's quack doesn't echo. Or at least one person that I was talking to seems to have thought that. It almost sounds as if it would make sense, one of those semi-plausible factoids that they always have in the children's section of popular science publications, and I could just imagine some sort of explanation about wave lengths cancelling each other out, or maybe even a less reasonable (yet 100% scientific) explanation that you don't actually "hear" a duck "quack", it's merely an impression, or maybe some drivel about how ducks are just opening their bills and the sound is provided by their friends. So I thought about the problem, certain that if I set my mind to it, I could reason the whole thing out, much as the ancient Greeks were able to deduce the size and shape of the Earth merely by being logical about their observations.

And the result was that a duck's quack does echo because I have heard it do so thousands of times in the Public Gardens right here in Halifax. There are lots of ducks in the pond and a big hotel across the road. In fact, if you're anywhere near South Park and Spring Garden in the evening, when traffic dies down, you should hear nothing but the echo of ducks.