MEANS OF EXPRESSION
Another innocuous species, the Dasypeltis of South Afri-
ca, blows itself out, distends its neck, hisses and darts
at an intruder.24 Many other snakes hiss under similar
circumstances. They also rapidly vibrate their protruded
tongues; and this may aid in increasing their terrific
Snakes possess other means of producing sounds
besides hissing. Many years ago I observed in South
America that a venomous Trigonocephalus, when dis-
turbed, rapidly vibrated the end of its tail, which strik-
ing against the dry grass and twigs produced a rattling
noise that could be distinctly heard at the distance of
six fect.2n • The deadly and fierce EcMs carinata of India
produces " a curious prolonged, almost hissing sound "
in a very different manner, namely by rubbing " the
sides of the folds of its body against each other/-' whilst
the head remains in almost the same position. The
scales on the sides, and not on other parts of -the bod}',
are strongly keeled, with the keels toothed like a saw;
and as the coilcd-np animal rubs its sides together, these
grate against each other.20 Lastly, we have the well-
known case of the Rattle-snake. He who has merely
shaken the rattle of a dead snake, can form no just idea
of the sound produced %y the living animal. Professor
Shaler states that it is indistinguishable from that made
by the male of a large Cicada (an ITomoptcrous insect),
which inhabits the same district.27 In the Zoological
21 Mr. ,T. Mansel Weale, ' Nature,' April 27, 1871, p. 50R.
35 ' .Tom-rial, of Ileson.rc.hes during' the Voyag-p. of the
" Beag-le," ' 1845, p. 96. T have compared the rattling- thus
produced with that of the Rattle-snake.
20 See the account by Dr. Anderson, Proc. Zool. Soc.
1871, p. 196.
" The ' American Natiiralist,' Jan. 1872, p. 32. T regret
that I cannot follow Prof. Shaler in believing- that the
rattle has "been developed, by the aid of natural selection,
for the sake of producing- sounds which deceive and at-
tract birds, so that they may serve as prey to the snake.