true for the curious predilection which Hans appeared to
have for the numbers from 2 to 4, especially for 3 (see page 68). As a
matter of fact the cause of this lies in nothing other than the
inadequate concentration of attention on the part of the questioner and
less often in an extravagant expenditure of concentration, which
explodes immediately after the first tap on the part of Hans (as in the
case of my first tests); but usually the cause lay in a complete lack of
concentration, though the same result may be produced by various causes.
It is usually after 2 to 4 taps of the horse's foot that the questioner,
who does not concentrate, makes his first move which naturally puts an
end to the tapping on the part of the horse. As a rule this jerk follows
immediately upon the second tap. (On the other hand, relaxation of
attention is very difficult upon the first tap. See page 95). The
questioner, however, would expect further tapping and therefore would
not bring his body back to a completely erect position and the result
would be a 3, the last unit of which would be given by the final tap
with the left foot. Here we also obtained light as to the answers which
Hans gave in those tests in which the method was that of "procedure
without knowledge". These responses had nothing to do with the problem,
for neither the horse nor any one else knew the solution. But in the
horse's responses the degree of tension of the questioner's
concentration was faithfully mirrored. An experimenter who was as
skillful in concentrating as Mr. von Osten, obtained--almost without
exception--very high numbers, whereas one whose concentration was slight
would receive in response to nearly all questions the answers 2, 3 or 4.
Thus, the Count zu Castell received in response to seventeen questions
the answer 2, three times, the answer 3, six times, and the answer 4,
four times, two answers being accidentally correct.

Another group of errors was characterized as stubbornness on the part of
Hans, such as his persistence in repeating an incorrect response, or his
repetition of a former correct answer in response to later questions
where it was perfectly senseless. During a demonstration before a large
number of persons, I held a slate with the number 13 upon it within the
horse's view and also within view of the spectators. I, myself, did not
know what number was written on the slate. Having been asked to tap the
number, Hans responded by tapping 5. T