The Clever Hans effect is a pernicious form of confirmation bias. The name comes from a horse, Clever Hans, who could be asked complex mental tasks and answer consistently and correctly by tapping his hoof. To spoil the ending, it was found that all he was doing was reading the questioner’s body language, which would change when he had given the right answer, and stop tapping his hoof.

Haha, funny story. But it’s a good thing we don’t really rely on horses for math calculations, right? Well, it turns out the same thing can happen with drug-sniffing dogs.