The best known sounding apparatus is that of the Rattlesnakes, described on p. 20. When alarmed, these snakes gather the body in a few coils or roll themselves up in a spiral, with the tail erect in the centre, and vibrating with great rapidity, whilst the head is ready for attack. Other snakes, such as the _Ancistrodon_ and some species of _Coluber_ and _Zamenis_, when excited, vibrate the tail in the same manner; but, being deprived of the sound-producing apparatus, this expression of their anger does not attract the same attention. It is from such a habit, however, that the rattle must have been evolved and perfected, not necessarily in a Lamarckian sense, but through the different steps by which evolution or creation has proceeded; _Natura non fecit saltus_, as Linnæus well said. Many suggestions have been made as to the use of the rattle. One of them is that the rattling resembles the sound made by locusts, and serves to decoy insect-eating birds; another, that it serves to call the sexes together. Probably it is useful to the snake as a warning to keep off disturbers which cannot serve as food, and thus prevents useless expenditure of venom, or even the breaking of the fangs. At any rate, it gives expression to the snake's excitement, as does the voice in the case of many other animals, and it seems reasonable to suppose that it may be applied to different purposes. With the advent of man, this means of attracting attention must tend to the more rapid extermination of the snakes which possess it. Another curious behaviour is that of feigning death, as observed in a harmless but vicious-looking snake, _Heterodon_, often called Puff-adder in America. It looks more like a Viper than a harmless snake, and when disturbed hisses loudly and flattens out the anterior part of the body, much as does a Cobra, and pretends to strike, although it is one of the few snakes that never bite man. If, however, this display proves of no avail in frightening away the intruder, the snake rolls on its back and opens its mouth, and then lies for a time, which may exceed a quarter of an hour, absolutely motionless, as if dead. As soon as it thinks the danger over, it awakens from its spasm and rapidly moves off. It is the opinion of those who have most experience of this snake that this extraordinary behaviour is not to be explained as a convulsion or faint due to fright, but constitutes a deliberate trick to save its life. Individuals of the South African Ringhals (_Sepedon hæmachates_) and of the Common Grass-snake have also been observed to feign death. The notion that snakes fascinate their prey, attracting it or reducing it to immobility by a mysterious power in their glittering eyes, is pure fable. Animals placed in a cage with a snake evince no particular fright, and fly away when pursued, if not actually turning round to defend themselves. It is even dangerous to offer a good-sized snake a wild rat for food, as all keepers of menageries know.