Chameleons and some other lizards inflate themselves when angry. Thus a
species inhabiting Oregon, the _Tapaya Douglasii_, is slow in its
movements and does not bite, but has a ferocious aspect; when
irritated it springs in a most threatening manner at anything pointed
at it, at the same time opening its mouth wide and hissing audibly,
after which it inflates its body, and shows other marks of anger. [422]
Several kinds of snakes likewise inflate themselves when irritated. The
puff-adder (_Clotho arietans_) is remarkable in this respect; but I
believe, after carefully watching these animals, that they do not act
thus for the sake of increasing their apparent bulk, but simply for
inhaling a large supply of air, so as to produce their surprisingly
loud, harsh, and prolonged hissing sound. The Cobras-de-capello, when
irritated, enlarge themselves a little, and hiss moderately; but, at
the same time they lift their heads aloft, and dilate by means of their
elongated anterior ribs, the skin on each side of the neck into a large
flat disk, the so-called hood. With their widely opened mouths, they
then assume a terrific aspect. The benefit thus derived ought to be
considerable, in order to compensate for the somewhat lessened rapidity
(though this is still great) with which, when dilated, they can strike
at their enemies or prey; on the same principle that a broad, thin
piece of wood cannot be moved through the air so quickly as a small
round stick. An innocuous snake, the _Trovidonotus macrophthalmus_, an
inhabitant of India, likewise dilates its neck when irritated; and
consequently is often mistaken for its compatriot, the deadly
Cobra.[423] This resemblance perhaps serves as some protection to the
Tropidonotus. Another innocuous species, the Dasypeltis of South
Africa, blows itself out, distends its neck, hisses and darts at an
intruder.[424] Many other snakes hiss under similar circumstances. They
also rapidly vibrate their protruded tongues; and this may aid in
increasing their terrific appearance.
Snakes possess other means of producing sounds besides hissing. Many
years ago I observed in South America that a venomous Trigonocephalus,
when disturbed, rapidly vibrated the end of its tail, which striking
against the dry grass and twigs produced a rattling noise that could be
distinctly heard at the distance of six feet.[425] The deadly and
fierce _Echis carinata_ of India produces a curious prolonged, almost
hissing sound in a very different manner, namely by rubbing the sides
71