140 THE BOOK OF A NATURALIST 
insect-catching organ, a decoy, a tactile organ, and, 
in some mysterious way, an organ of intelligence. 
And, after all, it is none of these things, and the 
way is still open for fresh speculation. 
I have on numberless occasions observed the 
common pit-viper of southern South America, 
which is of a sluggish disposition, lying in the sun 
on a bed of sand or dry grass, coiled or extended at 
full length. Invariably, on approaching a snake of 
this kind, I have seen the tongue exserted; that 
nimble, glistening organ was the first, and for 
some time the only sign of life or wakefulness in 
the motionless creature. If I stood still at a dis- 
tance of some yards to watch it, the tongue would 
be exserted again at intervals; if I moved nearer, 
or lifted my arms, or made any movement, the 
intervals would be shorter and the vibrations more 
rapid, and still the creature would not move. Only 
when I drew very near would other signs of excite- 
ment follow. At such times the tongue has scarcely 
seemed to me the “mute forked flash” that 
Ruskin calls it, but a tongue that said something, 
which, although not audible, was clearly understood 
and easy to translate into words. What it said or 
appeared to say was: “I am not dead nor sleeping, 
and I do not wish to be disturbed, much less 
trodden upon; keep your distance, for your own 
good as well as for mine.” In other words, the 
tongue was obtruded and vibrated with a warning 
purpose. 
Doubtless every venomous serpent of sluggish 
