At first sight it seems extraordinary that poisonous serpents, so dreaded by and so irresistible to most animals, should be so utterly helpless before the few creatures that prey on them.  But the explanation is easy.  Any highly specialized creature, the higher its specialization, is apt to be proportionately helpless when once its peculiar specialized traits are effectively nullified by an opponent.  This is eminently the case with the most dangerous poisonous snakes.  In them a highly peculiar specialization has been carried to the highest point.  They rely for attack and defence purely on their poison-fangs.  All other means and methods of attack and defence have atrophied.  They neither crush nor tear with their teeth nor constrict with their bodies.  The poison-fangs are slender and delicate, and, save for the poison, the wound inflicted is of a trivial character.  In consequence they are helpless in the presence of any animal which the poison does not affect.  There are several mammals immune to snake-bite, including various species of hedgehog, pig, and mongoose—­the other mammals which kill them do so by pouncing on them unawares or by avoiding their stroke through sheer quickness of movement; and probably this is the case with most snake-eating birds.  The mongoose is very quick, but in some cases at least—­I have mentioned one in the “African Game Trails”—­it permits itself to be bitten by poisonous snakes, treating the bite with utter indifference.  There should be extensive experiments made to determine if there are species of mongoose immune to both cobra and viper poison.  Hedgehogs, as determined by actual experiments, pay no heed at all to viper poison even when bitten on such tender places as the tongue and lips and eat the snake as if it were a radish.  Even among animals which are not immune to the poison different species are very differently affected by the different kinds of snake poisons.  Not only are some species more resistant than others to all poisons, but there is a wide variation in the amount of immunity each displays to any given venom.  One species will be quickly killed by the poison from one species of snake, and be fairly resistant to the poison of another; whereas in another species the conditions may be directly reversed.

The mussurama which Doctor Brazil handed me was a fine specimen, perhaps four and a half feet long.  I lifted the smooth, lithe bulk in my hands, and then let it twist its coils so that it rested at ease in my arms; it glided to and fro, on its own length, with the sinuous grace of its kind, and showed not the slightest trace of either nervousness or bad temper.  Meanwhile the doctor bade his attendant put on the table a big jararaca, or fer-de-lance, which was accordingly done.  The jararaca was about three feet and a half, or perhaps nearly four feet long—­that is, it was about nine inches shorter than the mussurama.  The latter, which I continued to hold in my arms, behaved with friendly and impassive indifference, moving easily to and fro through my hands, and once or twice hiding its head between the sleeve and the body of my coat.  The doctor was not quite sure how the mussurama would behave, for it had recently eaten a small snake, and unless hungry it pays no attention whatever to venomous snakes, even when they attack and bite it.  However, it fortunately proved still to have a good appetite.