proved that the increased rapidity in tapping in the case of
large numbers, which many regarded as an evidence of high intelligence,
(see page 20), was, as a matter of fact, brought about in the way
described. The two series (in each of which the time measured was for 10
taps) are quite in accord. The horse did not tap faster because he had
been given a large number by Mr. von Osten, but because the latter had
bent farther forward.

From all this it readily appears why it was possible to cause Hans to
increase his rate of tapping but not to decrease it. To do the latter
would involve a decrease in the angle of inclination of the body. This
would necessitate the erection of the body. As we have seen, this was
the signal to which Hans reacted by ceasing to tap. And as a matter of
fact we never knew the horse to decrease his rate of tapping in the
course of any single test, except in the case of very large numbers, and
then it was probably due to fatigue. Mr. von Osten insisted that Hans
often slowed down toward the end of a test, "in order to obviate
mistakes", but all the tests in which he tried to demonstrate this to
us, were unsuccessful. In spite of all exhortation, Hans would tap
either uniformly or somewhat more rapidly as soon as his master--in all
probability unconsciously--bent somewhat lower. Only once was such a
test successful. Mr. von Osten--upon our request--asked the horse to
give a certain large number. In this instance the decrease in the rate
of tapping was due to fatigue and had nothing whatever to do with the
desire on the part of the horse to avoid error. Furthermore, Mr. Hahn,
who had visited Hans twenty times and had made careful notes of his
observations, corroborated my statement when he said that he himself
never noted the decrease in rate mentioned. Contrary statements may
perhaps be due to the fact that the tense state of expectancy on the
part of the observer made the interval between the last taps appear
subjectively somewhat longer.

So much for the technique of the tapping. Now a word about the numbers
which Hans tapped. (I refer only to the results obtained in series which
involved no volitional control). The number 1 was very difficult to get.
Hans usually tapped 2 instead. Thus even in the case of Mr. von Osten he
responded five times with 2, and only in the sixth test did he react
correctly. As far as other questioners were concerned, 1 was seldom
ever obtained, except in the case of M