um... I think I pointed that very fact out a few pages back and then again yesterday and probably the day before.
I know.
Let me try to explain this.
Dog is sniffing around. Dog hits on scent (any scent) and the handler tells dog to follow. Dog follows scent. Handler is trained to follow dog and watch for visual clues from dog as well as visual evidence that what he is following is what he wants to follow. He finds foot prints or animal drippings etc that is a good clue.
Some dogs scent for nothing at all but human skin cells. Any human skin cells they are told to scent, they start, they alert when they find a scent and they follow it. Same thing the handler is looking for clues at same time. HAndler might realize hey we are following the scent of Gliniewicz here based on clues. We are following some first responder. ETC.
Some dogs scent for ground disturbance whether animal, human, vehicle,They can smell broken vegetation, kicked up dust,. This is where helicopters can be really bad.
This is how a canine can scent without knowing exactly what they are scenting. They are merely following a scent and the human has to determine whether that scent is important.
They also could have followed the scent of pepper spray if sprayed. Or of gun powder if they thought they suspects shot a gun. ETC...