Clever Hans: How a 'Psychic' Horse Revolutionized Scientific Method

In the early twentieth century, a horse in Berlin named Clever Hans became an unlikely architect of modern scientific rigor. Believed by crowds and credentialed observers alike to possess genuine mathematical reasoning, Hans was eventually revealed by psychologist Oskar Pfungst to be reading the involuntary body language of those around him — not solving problems, but sensing when humans expected him to stop. The scandal was not one of deception but of self-deception, and the lesson it forced upon science — that belief shapes observation, and observation must therefore be shielded from belief