Gunther informs me, it cannot swallow the frog, which thus escapes being devoured.
 `Dictionary of English Etymology,' p. 403.
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."
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. This resemblance perhaps serves as some protection to the Tropidonotus.
 See the account of the habits of this animal by Dr, Cooper, as quoted in `Nature,' April 27, 1871, p. 512.
 Dr. Gunther, `Reptiles of British India,' p. 262.
Another innocuous species, the Dasypeltis of South Africa, blows itself out, distends its neck, hisses and darts at an intruder. 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. 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 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 body, are strongly keeled, with the keels toothed like a saw; and as the coiled-up animal rubs its sides together, these grate against each other. 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 by the living animal. Professor Shaler states that it is indistinguishable from that made by the male of a large Cicada (an Homopterous insect), which inhabits the same district. In the Zoological Gardens, when the rattle-snakes and puff-adders were greatly excited at the same time, I was much struck at the similarity of the sound produced by them; and although that made by the rattle-snake is louder and shriller than the hissing of the puff-adder, yet when standing at some yards distance I could scarcely distinguish the two. For whatever purpose the sound is produced by the one species, I can hardly doubt that it serves for the same purpose in the other species; and I conclude from the threatening gestures made at the same time by many snakes, that their hissing,--the rattling of the rattle-snake and of the tail of the Trigonocephalus,--the grating of the scales of the Echis,--and the dilatation of the hood of the Cobra,-- all subserve the same end, namely, to make them appear terrible to their enemies.