Fig. 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.
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 c2 d, back to its original position. Hans has again made a "mistake" in his answer,—this time by one unit too few.
Fig. 4.