142 THE BOOK OF A NATURALIST 
lies motionless in the path, he certainly sees it, but 
without distinguishing it as a serpent. The vari- 
coloured surface it rests on and with which it is 
in harmony is motionless, consequently without 
animal life and safe to tread on—a rough flooring 
composed of mould, pebbles and sand, dead and 
green herbage, withered leaves, twisted vines, and 
sticks warped by the sun, brown and grey and 
mottled. But if the smallest thing moves on that 
still surface, if a blade trembles, or a minute insect 
flutters or flies up, the vision is instantly attracted 
to the spot and concentrated on a small area, 
and as by a flash every object on it is clearly seen, 
and its character recognised. Those who have 
been accustomed to walk much in dry, open places, 
in districts where snakes are abundant, have often 
marvelled at the instantaneous manner in which 
something that had been previously seen as a mere 
strip or patch of dull colour on the mottled earth, 
as a part of its indeterminate pattern, has taken 
the serpent form. And when once it has been 
recognised as a serpent it is seen so vividly and 
in such sharp contrast to its surroundings as to 
appear the most conspicuous and unmistakable 
object in nature. Why, in such cases, they ask in 
astonishment, did they not recognise its character 
sooner? I believe that in such cases it is the 
suddenly exserted, glistening, vibrating tongue that 
first attracts the eye to the dangerous spot and 
reveals the serpent to the mind. 
This warning character is, I believe, as has 
