Certain it is, that by the muscular power of the tail snakes perform wonderful feats, not only erecting themselves, and maintaining their balance for a short time, as a long pole is balanced by an acrobat on his chin or his nose; hanging by an inch or so of the tip, as an acrobat hangs for a time on one foot or one finger; raising themselves against a smooth surface, as you see the large pythons at the Gardens do against the smooth sides or glass fronts of their cages, even to the very top, but springing, ‘executing leaps,’ as Roget and others term it. For though the ‘leap’ is not strictly like the action of a frog or a grasshopper, or a man whose two limbs act in concert and together, the result is the same,—the reptile accomplishes a long distance with quickness, decision, and aim. Professor Owen[59] calls it a saltatory motion, ‘the sudden extension of the coils of the body reacting upon the point of earth on which the tail presses, throwing the serpent forward.’ Sometimes, when the creature lies closely coiled, the sudden unbending has the effect of a spiral spring; and occasionally, when the tail is brought suddenly up to the head, and the serpent springs forward again, and continues to do this in pursuit, as has often been witnessed, the effect is that of a rolling hoop, and has given rise to a belief among the ignorant that the reptile really rolls along. One in America, known as the ‘Hoop snake,’ is reported to ‘roll down hill,’ the idea originating possibly from the optical illusion in consequence of the rapid changes of position—an effect which we see in that amusing toy, the zoetrope. The ‘black snake’ of Australia, _Hoplocephalus pseudechis_, is one of the very active venomous kinds, whose motions in pursuit or escape are almost like leaps, and present the appearance of a hoop or circle. Reputed ‘hoop snakes’ are there also. The reptile rapidly extends itself to full length, then brings up its posterior portion in a loop, and so springs forward again, continuing to do this with amazing rapidity.