19. Clever Hans the counting horse changed the scientific method forever in 1907
In the early 20th century, Clever Hans the horse amazed people across Germany. Touring the country with his trainer, Wilhelm von Osten, Hans showed a staggering intellectual ability. People watched, mouths agape, as Hans added, subtracted, divided, and multiplied. He also read, spelled words, and understood German. Eventually, the intelligentsia took note, and examined Hans and Wilhelm. Led by Oskar Pfungst, the Hans Commission found that Hans actually responded to his trainer’s unconscious visual cues. Though Hans didn’t turn out to be as clever as people thought, his story changed the scientific method. Ever since, psychological tests have been double-blind.