The Puff-adder of Africa, when roused, will breathe in air and puff itself out to an extraordinary extent. Being, like all these cold-blooded creatures, very fond of warmth, it often comes at night to fires made by herdsmen or travellers; and so it happened that a traveller in South Africa, sleeping soundly one night beside the fire, wrapped in his cloak, was awakened by a weight on his chest, and found to his horror that a puff-adder had coiled itself up inside his shirt. His first thought was to seize the unwelcome visitor and throw it from him, but remembering that it probably would only injure him if disturbed, he had the presence of mind to let it remain in the warm nest it had found for itself, until, roused by a light, it slowly uncoiled itself and crept away. Of the serpents which are dreaded--not for their bite, for they have no poison-fangs--but for their great strength and daring, and for the way in which they coil round their victims, crushing them to death in their terrible embrace--the most dangerous are the Python of the Old World, and the Boa-constrictor of the New. In one respect all serpents are boa-constrictors, for a very small one has been seen in the act of thus crushing a bird; but the great boa which inhabits tropical America is a giant, which has been known to swallow even a buffalo whole, after it has crushed it to mummy, and broken all its bones. Boas can swim and climb; they will catch fish as they come near the surface of the water, and drag them ashore; or hang by their tails from some forest tree, and thus lie in wait to seize any animal which may be passing. They are now very shy of men, and not much feared by them; but these great snakes used to be worshipped as gods by the people of Mexico, and some of their serpent-idols have been found in ancient temples--showing how much they were once dreaded; for it is the habit of men to worship what they greatly fear.