ter it. This is
shown by the fact that one might remain just as silent while the horse
was tapping his answer as during the putting of the question and yet
obtain a correct response. Hans, furthermore, could scarcely be
distracted by auditory stimulations. If either the experimenter or
anyone else present sought, at a given moment, to interrupt him by such
calls as "Halt", "Wrong", etc., while he was going through the process
of tapping, they very seldom succeeded in their attempt. Even though
such interruption did succeed in seven out of the twenty-one cases in
which it was tried, the assumption is well grounded that the success was
due entirely or almost entirely to minimal movements involuntarily
executed by those attempting the interruption. It is to such minimal
movements that the horse, as we shall see later, promptly reacted. When
the experimenter (Pfungst), himself, made the interjections, which
certainly should have been more effective, we found that the horse was
actually disturbed in only two of the fourteen cases; and finally in ten
consecutive cases of attempted interruption not a single one was
successful. There was almost a complete absence of any ear movements on
the part of the horse, a fact in which I have been borne out by Mr.
Henry Suermondt, the distinguished horseback rider. Indeed, I cannot
recall that Hans ever turned his ears toward me, a fact which is
strikingly curious in the case of a horse so attentive and so spirited
in temper.

Finally, I might also mention that the breathing of the experimenter in
no wise influenced the outcome of the experiment. Whether he held his
breath or breathed on the leg or body of the horse, made no difference.

Investigations of the other senses became needless, for I had, in the
meantime, succeeded in discovering the essential and effective signs in
the course of my observations of Mr. von Osten. These signs are minimal
movements of the head on the part of the experimenter. As soon as the
experimenter had given a problem to the horse, he, involuntarily, bent
his head and trunk slightly forward and the horse would then put the
right foot forward and begin to tap, without, however, returning it each
time to its original position. As soon as the desired number of taps was
given, the questioner would make a slight upward jerk of the head.
Thereupon the horse would immediately swing his foot in a wide circle,
bringing it back to its original position. (This movemen