The dogs are trained to react when the officer is interested, because the handler is the one who hides the drugs, and rewards the dog when he finds the drugs. Except the officer knows where the drugs are, so the dog simply learns how to read the K9 Handler.
Drug sniffing dogs are worse than chance, this is not nefarious it’s just bad animal training. The owner of Clever Hans was NOT a con-man, he just was unaware that Hans was reading HIM when he got close to the correct number.
Also I love the “If you don’t have drugs in your ass you have nothing to worry about!” Yeah how about your vehicle being tossed, your body being searched, and unwanted X-rays, and possibly probing hands in your fart box?
That is not my idea of a fun evening.