[S] In a special series of experiments a subject was instructed to execute rapid head movements as minute and as evenly as possible. These were registered objectively and at the same time I made judgments concerning them. The results showed that my judgments were most exact in the case of the most minute jerks. The thing that made it especially easy to judge the movements of Mr. von Osten under normal conditions, ([page 220]), was their extraordinary evenness, such as I have not met with in any other individual.
CHAPTER V
EXPLANATION OF THE OBSERVATIONS
The author having described the observations made upon the horse, and having discussed the activities of the questioner upon the basis of observations made objectively and upon his own introspections, and having verified the results thus obtained, by means of laboratory tests,—we are now in a position to solve satisfactorily all the problems which this interesting case has presented.
That which is least difficult to understand is the horse's seeming knowledge of language and particularly his ability to answer questions, no matter by whom, or in what dialect, they were put. As a matter of fact, it made no difference who desired an answer, for the only person upon whom the experiment depended was the questioner, that is, the one who asked the horse to tap. We have everywhere designated this person as the experimenter or questioner. It was he who gave the directions, and since all that were involved were visual signs, the drama in which Hans appeared as the hero, was nothing but a pantomime. All speech was superfluous and, except in so far as the tone of voice in which it was spoken was soothing or reprimanding, it was quite unintelligible to the horse.
From the foregoing, the reader understands without further explanation Hans's ability to count and to make computations. If the number of taps had depended solely upon the length of time and the angle at which the questioner bent forward, the horse would have been able to tap any number desired. Since, however, only the right foot was employed, the left one being used at most for making a final tap, the number of taps had an upper limit which was due to the fatigue of the animal. This limit was about 100. That it was possible to ask such questions as: "How many times is 100,000 contained in 654321?", and thus to give problems involving millions, is perfectly clear.
All wonderful feats of counting and computation which were accomplished while thus experimenting with the horse are to be accredited, not to the horse, but to the questioner. If such is the case, they certainly cannot be considered astonishing. Thus, when to the question, "How many of the gentlemen present are wearing straw hats?" the horse answers correctly in accordance with the wording of the question and omits the straw hat of a lady, then Mr. von Osten is the guide. It is no wonder that Hans never showed the slightest excitement when confronted with difficult problems, nor that it apparently took no time whatever to solve them.
Hans, however, was also a faithful mirror of all the errors of the questioner. Aside from mistakes due to occasional interruptions on the part of visitors, these errors had two sources: faulty computation and inadequate concentration—i. e., aside from arithmetical errors on the part of the questioner, were his premature or belated movements. Since both of these factors might be operative, the following three possibilities arise.