EXPERIMENTS AND OBSERVATIONS 59 



foot. The curve, therefore, has a kink at b, and the back- 

 step occurs with seeming hesitancy, — Hans appears not 

 quite certain of his result. 



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. 



Finally, if the signal be deferred still longer, it becomes 



Fig. 3. 



impossible to prevent the extra tap. The back-step again 

 has the same form as in figure i ; 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^ d, back to its original position. 

 Hans has again made a " mistake " in his answer,— this 

 time by one unit too few. 



All these variations go to show one thing : Hans never 



