EXPERIMENTS AND OBSERVATIONS 47 



see later, promptly reacted. When the experimenter 

 (Pfungst), himself, made the interjections, which cer- 

 tainly 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 es- 

 sential and effective signs in the course of my observa- 

 tions of Mr. von Osten. These signs are minimal move- 

 ments 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 for- 

 ward 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, bring- 

 ing it back to its original position. (This movement, 

 which in the following exposition we shall designate as 

 "the back step", was never included in the count.) 



