The Curious Case of Clever Hans

Credit: Wiki Commons/public domain

You may think your dog or cat is smart and amazing, but it's got nothing on a horse that drew huge crowds in Germany and throughout Europe over a century ago.

The horse, named Clever Hans, was known around the world for his inexplicable abilities. William Von Osten put his amazing horse on display in 1891, and together he and Hans treated crowds to sights never before seen.

Not only could Hans count -- something no other animals were said to do -- but he could also tell time, read, and spell (in German, of course).

Since the horse couldn't speak (that would have been a remarkable feat indeed), he communicated mainly by stamping one foot on the ground. If Hans was asked what five and two added up to, he would tap seven times; if he was asked what day came after Monday, he would be told to tap once for Tuesday, twice for Wednesday, and so on.


Clever Hans was examined by a group of researchers led by a philosophy professor named Carl Stumpf. What was the secret -- if indeed there was one? Was it all a hoax or trick? Or was this a truly unique horse, a pillar of equine intellect that could rival any schoolchild -- or at least an elected official?

In 1904 the group issued a statement saying that they could find no evidence of trickery. However Prof. Stumpf and one of his students, Oskar Pfungst, would finally solve the mystery. They noticed that Hans could rarely answer questions that Von Osten did not know the answer to, suggesting that that there must be some link between the two.

Through careful testing and observation they realized that Hans was responding to unconscious cues from his trainer. For example when Hans was asked to add two and three, von Osten or another questioner (standing right in front of Hans watching him closely) would lean forward slightly after Hans had tapped the fifth time but before he could tap a sixth.

Von Osten had been watching Hans, but Hans had been watching Von Osten just as closely. Each time the horse would reach the correct number of taps to provide human-like knowledge about the day of the week, what a word meant, or a mathematical answer, his trainer would make subtle movements (sometimes merely a change in facial expression, or a shift of stance) that would cue Hans to stop.

The horse was of course rewarded for correct answers, which reinforced this behavior. Clever Hans was indeed clever -- but much less so than Von Osten and the public believed.

The Clever Hans story and its discovery of unconscious cueing is still discussed among psychologists and animal communication experts. In fact a recent study found that dogs follow cues from their owners’ facial expressions.

As Jennifer Viegas reported here on Discovery News, a recent study explained that

Dogs often seem to be psychic, anticipating what we're going to say or do, and now research reveals one secret behind this canine ESP: Dogs intensely track our eye movements, which can be tied to intent. Human babies also possess the ability, described in the latest Current Biology.... "Dogs are receptive to human communication in a manner that was previously attributed only to six-month-old human infants," co-author Jozsef Topal told Discovery News." They read our intention to communicate in a preverbal, infant-like manner," added Topal, who works in the Institute for Psychological Research at the Hungarian Academy of Sciences.
Of course Clever Hans knew this back in the 1890s.

Discovery News