A medical student, an Internist, a Psychiatrist, a Surgeon and a Pathologist go duck hunting.
They barely find their duck blind before the first duck flies over.
The medical student is the first to raise his shotgun, but unable to tell if the duck is really a duck, he does not shoot.
The internist aims his shotgun, but can not tell if the duck is male or female and he does not shoot.
The psychiatrist has the duck framed in his sight, but then lowers his shotgun, claiming "I know this is a duck, but does the duck know he's a duck?"
The surgeon quickly raises his shotgun, aims, and without pause shoots. The duck falls to the ground. The surgeon turns to the pathologist. "Go figure out if that's a duck or not."