A general practitioner, an internist, and a surgeon go duck hunting. A bird flies over, the GP jumps up and says “Well, it looks like a duck and flies like a duck. Must be a duck.” He blasts away 3 times with his shotgun, missing each time, and the bird flies on.
Another bird flies over. The internist looks up and says, “Well it looks like a duck and flies like a duck. But we can’t rule out an Aleutian Canada goose, which can appear similar. And since this is a federally endangered species, shooting it would be contra-indicated. Another consideration would be…” By the time he’s finished talking, the bird is out of range.
The third bird flies over. The surgeon takes one shot and the bird falls dead at his feet. He picks it up and says “What do you know. A duck.”