The Curious Case of Clever Hans

Long before Mr. Ed, the talking horse, Clever Hans was a horse who apparently could understand human language and answer mathematical questions.

In the late 1800s, a German high school mathematics instructor named Wilhelm Von Osten believed humans had underestimated animal intelligence and that animals could learn to read or count. Von Osten’s initial attempts were unsuccessful but a horse named Klude Hans learned a wide variety of skills. Hans could add, subtract, multiply, and divide; if Von Osten asked for the sum of 3 plus 2, the horse would tap his hoof five times.

Von Osten started showing off Hans’ mathematical abilities all over Germany. For example, Von Osten would ask Hans: “If the first day of the month is a Wednesday, what is the date of the following Monday?” Hans would respond with six taps of his hooves. The horse was soon known as Clever Hans and could answer questions with nearly 90% accuracy.

As Clever Hans’ fame grew, many claimed Von Osten was cheating and demanded an inquiry. The German board of education assembled the Hans Commission – two zoologists, a psychologist, a horse trainer, school teachers, and a circus manager – to conduct an investigation. The commission concluded the Clever Hans was legit; the horse could answer questions asked by anyone, even if Von Osten wasn’t there.

Eventually psychologist Oskar Pfungst figured out what was happening. During a series of experiments, Pfungst noticed that Clever Hans often didn’t know the correct answer when the questioner didn’t know it either. Furthermore, if the horse couldn’t see anyone who did know the answer, Hans didn’t respond correctly.

It turned out Clever Hans had learned to detect subtle nonverbal cues. After someone asked a question, Hans would begin tapping his hoof. When the horse reached the correct answer, the questioner would provide an involuntary clue such as tilting their head or tensing their muscles. Clever Hans would recognize this behavior and stop tapping. When Hans couldn’t see the cues, he couldn’t answer the question.

After the curious case of Clever Hans, scientists began to study nonverbal clues and discovered people can unconsciously communicate information to others through subtle movements. Even if you’re not aware you’re providing these clues, someone can be trained to pick up on your “tells.”

Expert poker players owe a debt to a horse named Clever Hans.

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