Doctors.
So a general practitioner, a paediatrician, a psychiatrist, a surgeon, and a pathologist all went on a duck hunt.
A bird flies over, and the gp takes aim, then says; "I'm not sure if that is a duck, better refer to a specialist" and the bird escapes.
The second bird comes over, and the paediatrician dithers also, about getting a second opinion, and that bird escapes.
The psychiatrist gets the third bird in his sights, then thinks, "I know that is a duck, but does it know it is a duck?" and of course, the bird escapes!
The surgeon spots the next bird, jumps to his feet, and barely taking aim, blasts it out of the sky, turns to the pathologist and says, "Go and see if that was a duck, will you?"
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