Three doctors are on a duck blind and a duck flies overhead. The general practitioner looks at it and says, 'Looks like a duck, flies like a duck, it's probably a duck,' 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, 'Hamm, green wings, yellow bill, quacking sound, might be a duck,' he raises his gun to shoot but the duck is well gone. A third bird flies overhead. The surgeon raises his gun and shoots almost without looking, bring the bird down, and turns to the pathologist and says, 'Go see if that was a duck,'