G. 2.]

If the signal be given somewhat later still (Fig. 3), i. e., when the
foot is being lowered to complete a tap, Hans is still able to put on
the brakes--as it were--and draw back his foot before it reaches the
ground. The whole process gives the impression that the horse was just
about to make a "mistake" of one unit, but at the last moment had
bethought himself of the correct answer.

[Illustration: FIG. 3.]

Finally, if the signal be deferred still longer, it becomes impossible
to prevent the extra tap. The back-step again has the same form as in
figure 1; Hans has made a "mistake" in his answer by one unit too many.

Conversely, if the head-jerk of the questioner occurs too soon; i. e.,
at the moment the horse has raised his foot for the final tap to the
height _b_, (Fig. 4), then the tap is not completed,--but the foot,
without touching the ground, makes the curve _b c_{2} d_, back to its
original position. Hans has again made a "mistake" in his answer,--this
time by one unit too few.

[Illustration: FIG. 4.]

All these variations go to show one thing: Hans never knows in advance
which tap is to be the final one. These variations in his reactions
occurred often without having been intended by the questioner. But to
bring them about at will required skill, on account of the shortness of
the time involved in the reaction.

Whenever the signal for stopping--which we have just discussed--was
followed by the complete erection of the head and trunk, Hans would
definitely cease tapping. If, however, the questioner failed to assume a
completely erect position, or if he stooped forward ever so slightly,
the horse would follow the back-step of the right foot with an extra tap
of the left foot. Besides occurring in tests in which Mr. von Osten
assumed the role of questioner, this fact was also noted when the Count
zu Castell and Mr. Schillings acted as subjects. Since the extra tap
just mentioned was not given like the others with the right foot
forward, but with the left foot upon the spot, it was possible for the
horse to execute it with a greater show of energy. This simulated a high
degree of mental certainty on the part of the horse, as if he wished to
indicate that this was the correct solution of the problem and it would
have to stand. In spite of all this, many errors would creep in. It was
possible to prolong this extra tap and thus make it appear more
dilatory. We need hardly add that henceforth it was