III THE SERVICE OF TAILS 95 
serpent; and are they aroused, this agitation be- 
comes very marked indeed. I do not suppose that 
the puma which lies in wait for the guanacos, and 
attracts them by his lifted tail as hunters some- 
times toll up the pronghorn by lying on their faces 
and kicking up their heels, thought that strategy 
out and put it into deliberate execution; but the 
waving of the tail was practically involuntary, and 
he has learned to adapt his hunting to a method 
whose success we can explain, but which he prob- 
ably never has fathomed or sought to fathom, for 
that matter. 
Serpents give a conspicuous example of this 
nervous condition of the tail. Every snake, when 
excited, elevates the tip of it, which is highly sen- 
sitive to touch, and vibrates it with more or less 
rapidity. This is most marked in the viperine 
species, and it is here that we find the horny tips, 
and the rattles of the rattlesnake, which can be 
agitated with such extreme rapidity as to make 
merely a fan of light—the eye cannot follow the 
motion — and can be sustained for hours. There is 
good reason to believe that the presence of the 
rattle is connected with, if not the result of, this 
maximum nervousness. How great the importance 
of this is in the economy of this kind of serpent, 
and the way in which it is important, I have en- 
deavored to show elsewhere! The rattling of the 
1 “ Rattlesnakes in Fact and Fancy,” — Chapter IX of my book 
“Country Cousins,” published by Harper & Brothers, New York, 1884. 
