EXPERIMENTS AND OBSERVATIONS 75 



direction is right? " or " Which way is upward? ", Hans 

 would execute all sorts of head movements without rhyme 

 or reason. It was evident that he noted that a head move- 

 ment of some kind was expected of him, but did not know 

 the particular one that was wanted. But if the questioner 

 now raised his head, Hans would begin to nod and would 

 continue doing so until the questioner lowered his head. 

 This reaction was interpreted as signifying " yes ". Mr. 

 von Osten had always asked Hans before each of the 

 more difficult tests whether he had comprehended the 

 meaning of the problem, and was reassured only upon 

 seeing the horse's affirmative response. But contrary to 

 Mr. von Osten's expectation, Hans also responded in this 

 manner after a pair of ear-caps had been drawn over his 

 ears. In the case of the tests described at the beginning 

 of the chapter, in which the method was that of "pro- 

 cedure without knowledge ", Mr. von Osten had always 

 insisted that we await Hans's nod of comprehension 

 before proceeding. We complied ; Hans nodded and — 

 regularly disgraced himself ! 



When the questioner raised his head somewhat higher 

 than normal, Hans would throw his own upward, which 

 was supposed to signify " upward ". A lowering of the 

 head on the part of the questioner was followed by a 

 lowering on the part of Hans, which was his form of re- 

 sponse for " down ". For some time I was in a quandary 

 as to the difference between the questioner's signal for 

 this latter response and the one which was the signal for 

 the horse to begin tapping, although I had often given 

 both kinds unwittingly. Further experiments showed 

 that Hans r«sponded with a nod of the head whenever 

 the questioner, while bending forward, chanced to stand 

 in front of, or to the side of the horse's head, but that 



