ANIMALS' ILLUSIONS 165 



twilight. In the absence of a hand, the sense of touch 

 is deficient in most animals. This deficiency, except in 

 the case of birds, is not compensated by special acuteness 

 of sight, though nearly all animals apply a sensible test 

 to ascertain whether an object is living or inanimate. 

 They wait to see if it moves ; and to do this they 

 know that the first condition is to keep absolutely still 

 themselves. Most of the larger birds, notably wood- 

 pigeons, remain perfectly motionless for many seconds 

 after alighting in a new place, in order to identify any 

 moving object. On the other hand, the power of scent 

 is a great corrective to animal misconceptions about 

 objects. It is their chief means of distinguishing the 

 animate from the inanimate, and is always employed by 

 them in the diagnosis of death. It would be interesting 

 to know whether camels and horses share the illusions 

 produced on men by mirage in the desert, or whether 

 they are all the time aware that the seeming lakes of 

 water are unreal. It is certain that they are frequently 

 mistaken in sounds, for there are many authenticated 

 instances in which animals have mistaken the mimicry 

 of parrots for the call of their masters, and a nervous 

 dog, which had a special dread of thunder, has been 

 known to go into a fit when it heard a sack of coals 

 being emptied into the cellar. 



