Three doctors are in the duck blind and a bird flies overhead. The general practitioner looks at it and says, Looks like a duck, flies like a duck…its probably a duck, and shoots at it but misses and the bird flies away.

The next bird flies overhead and the pathologist looks at it, then looks through the pages of a bird manual, and says, Hmmmm…green wings, yellow bill, quacking sound…might be a duck. He raises his gun to shoot it, but the bird is long gone.

A third bird flies over. The surgeon raises his gun and shoots almost without looking, brings the bird down, and turns to the pathologist and says, Go see if that was a duck.