to Hans in von Osten's absence
and which formed the initial number of some mathematical operation, was
tapped correctly. This may possibly be explained by the assumption that
this initial number had been retained in the memory of some of those
present, (see page 149, on the "perseverative tendency"), and that the
horse, since he had been working with some of them, responded to one of
those present. Chance may have played some part also.

[Footnote L: Mr. Schillings, however, did succeed in making a number
of tests with the co-operation of others who had never before worked
with the horse. These tests were made under the following
conditions: The horse was standing in his stall, when Mr. Schillings
and another gentleman approached him. There was no one else present.
Mr. Schillings, who tried to remain as passive inwardly, as
possible, asked his partner to think consecutively of different
numbers between one and 20, which thus were known to him alone. Hans
was then commanded by Mr. Schillings to tap the numbers, which he
did, to the great astonishment of the men, and especially of Mr.
Schillings. In like manner Mr. Sander, a staff physician in the
marine, received--so he writes me--three correct responses to four
questions which he put to the horse. It happened also in the case of
two scientific men and finally, too, in my own case when I first
came in contact with the horse, (see page 88). The horse's reaction
was brought about in the same way in every one of these instances.
Mr. Schillings, in bending forward slightly, thereby started the
horse a-tapping, and his companion--just as innocently--interrupted
the process by means of a movement of his head, when the right
number of taps was reached.

I later tried similar experiments together with Mr. Hahn. I was
aware of the answer to the riddle at the time, but he was not. Mr.
Hahn stepped in front of the horse and thought intently of certain
numbers. I did the questioning, that is, I got the horse to tap. In
twelve tests Hans responded correctly in only two instances. In the
ten others he always tapped beyond the number Mr. Hahn had in mind,
e.g., 21 instead of 2, and was evidently awaiting a movement on my
part. When we exchanged roles, Mr. Hahn doing the questioning and I
doing the "thinking," the horse would not respond at all, although
as a rule Mr.