EXPERIMENTS AND OBSERVATIONS 67 



sitate the erection of the body. As we have seen, this 

 was the signal to which Hans reacted by ceasing to tap. 

 And as a matter of fact we never knew the horse to 

 decrease his rate of tapping in the course of any single 

 test, except in the case of very large numbers, and then 

 it was probably due to fatigue. Mr. von Osten insisted 

 that Hans often slowed down toward the end of a test, 

 " in order to obviate mistakes ", but all the tests in which 

 he tried to demonstrate this to us, were unsuccessful. In 

 spite of all exhortation, Hans would tap either uniformly 

 or somewhat more rapidly as soon as his master — in all 

 probability unconsciously — bent somewhat lower. Only 

 once was such a test successful. Mr. von Osten — upon 

 our request — asked the horse to give a certain large 

 number. In this instance the decrease in the rate of 

 tapping was due to fatigue and had nothing whatever 

 to do with the desire on the part of the horse to avoid 

 error. Futhermore, Mr. Hahn, who had visited Hans 

 twenty times and had made careful notes of his observa- 

 tions, corroborated my statement when he said that he 

 himself never noted the decrease in rate mentioned. Con- 

 trary statements may perhaps be due to the fact that the 

 tense state of expectancy on the part of the observer made 

 the interval between the last taps appear subjectively 

 somewhat longer. 



So much for the technique of the tapping. Now a 

 word about the numbers which Hans tapped. (I refer 

 only to the results obtained in series which involved no 

 volitional control). The number i was very difficult to 

 get. Hans usually tapped 2 instead. Thus even in the 

 case of Mr. von Osten he responded five times with 2, 

 and only in the sixth test did he react correctly. As far 

 as other questioners were concerned, i was seldom ever 



