The brilliant coloring of poisonous snakes is sometimes set down by naturalists to "warning," but the details of coloring among reptiles have never been thoroughly worked out. The difficulty suggests itself that if the vivid yellows and oranges of some snakes are meant to warn off dangerous animals, the same conspicuousness would warn off the animals on which the venomous forms prey. Thus, while being hunted, a showy skin might be of advantage to the snake; in hunting it would be an equal disadvantage. But when one watches on the spot the manner in which snakes really do their hunting, it becomes probable that the coloring, vivid and peculiar as it is, in most cases is designed simply to aid concealment. One of the most beautiful and ornate of all the tropical reptiles is the puff-adder. This animal, the bite of which is certain death, is from three to five feet long, and disproportionately thick, being in some parts almost as thick as the lower part of the thigh. The whole body is ornamented with strange devices in green, yellow, and black, and lying in a museum its glittering coils certainly form a most striking object. But in nature the puff-adder has a very different background. It is essentially a forest animal, its true habitat being among the fallen leaves in the deep shade of the trees by the banks of streams. Now in such a position, at the distance of a foot or two, its appearance so exactly resembles the forest bed as to be almost indistinguishable from it. I was once just throwing myself down under a tree to rest when, stooping to clear the spot, I noticed a peculiar pattern among the leaves. I started back in horror to find a puff-adder of the largest size, its thick back only visible, and its fangs within a few inches of my face as I stooped. It was lying concealed among fallen leaves so like itself that, but for the exceptional caution which in African travel becomes a habit, I should certainly have sat down upon it, and to sit down upon a puff-adder is to sit down for the last time. I think this coloration in the puff-adder is more than that of warning, and that this semi-somnolent attitude is not always the mere attitude of repose. This reptile lay lengthwise, concealed all but a few inches, among the withered leaves. Now the peculiarity of the puff-adder is that it strikes _backward_. Lying on the ground, therefore, it commands as it were its whole rear, and the moment any part is touched, the head doubles backward with inconceivable swiftness, and the poison-fangs close upon their victim. The puff-adder in this way forms a sort of horrid trap set in the woods which may be altogether unperceived till it shuts with a sudden spring upon its prey.