"If it looks like a duck, walks like a duck and quack like a duck, then it just may be a duck."

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The party and the Krikkit warship looked, in their writhings, a little like two ducks, one of which is trying to make a third duck inside the second duck, whilst the second duck is trying very hard to explain that it doesn't feel ready for a third duck right now, is uncertain that it would want any putative third duck anyway, and certainly not whilst it, the second duck, was busy flying.

— Douglas Adams