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1.
If someone asks if an answer is correct, and its clearly obvious to everyone it is, then the retort is "do one legged ducks swim in circles?"
"Is the sky blue?"
"Do one legged ducks swim in circles?"
by Dubster May 25, 2003
 
2.
"She just bit my head off. She PMS-ing?"
"Do one legged ducks swim in circles?"
by redgyul September 23, 2004
 
3.
If someone is trying to proove a point , but really has no idea what they are arguing , they might use this phrase "Do one legged ducks swim in circles?", it will throw the opposition for a while until the realise that no they dont , that would be stupid , thus is only good for short term evasion.

subject change is recommended before they realise :)
Fred:"so you actually understand quantum physics??"
Sam:"Does a duck with one leg swim in circles??"
Fred:"umm ??"
Sam:"look at the weather!!"
..
..
much later ...
Fred :" hey wait a minute , no !!"
by Duck expert May 27, 2003