At the beginning of the 20th century, a horse named Hans lived in Germany. This Oryol trotter gained wide popularity due to the fact that he possessed the highest intellect and could perform arithmetic operations in his mind and solve other mathematical (and not only) problems, giving the correct answers to questions asked by people. Anyone could ask questions in front of the general public.
Hans belonged to Wilhelm von Austin, a mathematics teacher in one of the grammar schools, who became interested in the then gaining popularity of Darwin's theory and decided to find out how smart his horse was, which led to an absolutely amazing result. If you believe the surviving descriptions of representations, then Hans knew how to add, subtract, multiply and divide relatively large numbers, perform the same calculations with fractions, indicate the exact time, specific dates in the calendar, and even read and hear words and whole phrases in German. Hans answered all the questions with the number of strokes with his hoof on the ground. Among the questions to which he gave answers were not only such as "How much is 12 + 12?", But also, for example, "If the eighth day of the month falls on Tuesday, what day will be next Friday?" And, surprisingly, questions could be asked not only by von Austin and not only orally, but also in writing - Hans "read" the question and, with the help of his hoof, gave an answer to it. It should be noted that Hans did not give correct answers to absolutely all of the questions even of his master, not to mention the questions of other people, but the percentage of correct answers was amazingly high.
Soon Wilhelm von Austin was already giving whole street performances with his amazing horse, and after a while he began to ride with him throughout Germany, sometimes gathering real crowds of people for impromptu performances that were highly popular - perhaps not least because never took money from people for the right to look at a horse or ask him a question. After some time, an article about Hans was published in the American newspaper New York Times, after which the amazing horse gained relatively wide popularity all over the world and attracted the attention of scientists, among others.
In 1904, the Board of Education of the German Empire appointed a special commission, called the "Hans Commission", in order to verify the reality of rumors about the phenomenal mind of a horse, which, after conducting various tests with Hans, did not find any fraud, no matter how strange it may sound.
Some time after the verdict was passed, a later famous German psychologist began to work with Hans, and at that time also a student of Stumpf named Oskar Pfungst, who organized a much more serious study. The results were surprising: Hans almost always answered correctly only if he could see the questioner and if the questioner himself knew the answer to it.
Then Pfungst in his work began to pay more attention to the study of the behavior of the person asking the question, and came to the following conclusions: while slowly tapping his hoof after asking the question, Hans observes the expression on the face and posture of the questioner; when the number of knocks made by Hans equaled the correct answer to the question, the vast majority of people in one way or another showed excitement and tension (and at the moment of the correct answer, perhaps, on the contrary, a certain relaxation), being shocked by this, or at least just gazing at him, and this behavior "prompted" Hans that it was time to stop pounding his hoof. Horses may have more subtle ways of "socializing" than humans, and allow them to notice the slightest emotional reactions. In other words, Hans was really a phenomenally intelligent horse and perfectly understood what they wanted from him, but, of course, he did not know or understand either mathematics or German.
In addition to the owner of the horse, who piously believed in her mystical abilities, there was another person who strongly disagreed with the conclusion of Pfungst. This is the German merchant Karl Krall, who became interested in Hans during von Osten's life, and after the death of the owner bought a horse.
Krall taught Clever Hans to identify smells: a horse could not only distinguish, for example, mint from vanillin or carbolic acid from turpentine, but also “answer” the question “What is it” by choosing one of the options. Another amazing ability of Hans, discovered by Krall, is the ability to almost unmistakably recognize familiar people in portraits and photographs and "call" their names, as well as distinguish coins by denomination and playing cards by suits (although, of course, the latter can be explained simply by good visual memory). Finally, Krall even introduced Hans to geometry: the horse learned to distinguish intersecting and parallel straight lines, acute, right and obtuse angles from each other.
Subsequently, Krall bought three more horses: two Arab stallions, Mohammed and Tsarif, and a completely blind horse named Berto, which he taught at the same time as Hans. According to the researcher, all horses were able to tap their names out of letters, put together other words from letters, and sentences from words, and later even mastered conversations with the help of percussion.
Karl Krall described the results of his experiments in detail in the monograph "Thinking Animals", published in Germany in 1912. In it, describing his methods of training horses, he argued that these animals are actually intelligent - they can think and use abstract concepts. The most surprising part of the book was its ending: "In order to ensure my priority, I present below some conclusions that are the basis for my future experiences." Moreover, the further fragment of the text that ends the book was encrypted, and this cipher has not yet been solved; what Krall meant remains a mystery.