An internist, a psychiatrist, a surgeon, and a pathologist go duck hunting. A bird flies by. The internist raises his gun, aims, and thinks, I wonder if that's a duck. By which time, it's too late. The psychiatrist raises his gun aims, and thinks, I wonder if that duck knows he's a duck. The surgeon raises his gun, aims, and shoots the bird out of the air. He turns to the pathologist and says, Go see if that was a duck.