It occurred to Dennis now to attempt to trace the mark in the opposite direction, away from the point where it disappeared in the water. It speedily grew fainter as he came to harder soil, and he lost it altogether where it entered undergrowth which had no doubt been partially submerged when the marsh was at its highest. But after some search he found it again where it emerged from the rank vegetation, and from that point he traced it with little difficulty, for it kept fairly close to the margin of the lake. Its resemblance to the track of a wheel had now ceased; not even the most rickety of carts, driven by a drunken tranter on a Devonshire lane, could have made such erratic movements as must have caused this shallow winding mark on the soil. Dennis followed its curves with persistent curiosity, not unmixed with a vague uneasiness. Mirandola accompanied him, springing lightly from bough to bough of the trees nearest the edge of the marsh, descending with extraordinary quickness and loping along the ground where gaps intervened, or the fringe of the woodland belt took a trend inwards.
At length the tracking came perforce to an end. Again the trail disappeared into the water, and Dennis halted, feeling a little vexed that his patience was, after all, to bear no fruit. He looked round for Mirandola. The monkey had disappeared, exploring, no doubt, thought Dennis, a close-packed thicket that came within a few yards of the morass, having apparently crowded out all nobler trees save one slender cedar which, dominating the undergrowth, seemed taller than it really was.
Dennis was about to give up the problem as hopeless and go on his way, when suddenly he heard Mirandola chattering in a manner that was new to him. The moment after, the monkey sprang from the thicket into the tree, and climbed with frantic speed to the very top, where he sat gibbering and shaking with terror. Dennis, wondering what had perturbed him, took a step forward, then started back in a cold shiver. A huge serpent was rearing itself from the midst of the undergrowth and winding its coils about the trunk of the tree.
Mirandola on the topmost branch had now ceased his chattering, and clung, watching the monster with dilated eyes. The poor creature was helpless. To descend from his perch would have been fatal; there was no other tree at hand to which it might escape. Indeed, under the fascination of the serpent's baleful eyes, as it slowly drew its immense coils up the trunk, the monkey lost all power of motion; and Dennis himself, even with the thicket between him and the monster, felt a sort of chill paralysis as he watched its sinister movements. For half a minute he stood rooted to the spot; then, making an effort to throw off this dire oppression, he tried to think of some means of helping the monkey. At that moment of danger, he was conscious for the first time of the strength of his affection for the animal whose companionship had done so much to relieve the awful solitude of the island. Unless he intervened, Mirandola was doomed, and the thought of losing Mirandola filled him with a fierce longing to slay this monster that was crawling inch by inch towards its prey.
His first impulse was to run back to his hut for the gun he kept there ready loaded; but slow as the serpent's progress was, before he could return to the spot the tragedy would have ended. Then he remembered how the reptiles in the woods at home were killed. A blow on the vertebrae crippled them; could he cripple this huge creature, which even yet had not heaved all its length into the tree? His only weapon was the sailor's clasp-knife which he always carried at his girdle. He opened it impulsively, then hesitated. If he failed to hit the vertebrae, and dealt only a flesh wound, he might perchance save the monkey, but could he then save himself? He knew nothing of a boa constrictor's power of movement; yet his instinct told him that, if once enfolded in those monstrous coils, he must inevitably be crushed to death. But he could not stand and see his pet mangled and devoured: the serpent, moving deliberately, as though aware of its victim's paralysis, was not yet beyond his reach. Springing through the undergrowth, he marked a spot some distance from the reptile's tail. The serpent heard his approach, and turned its head slowly in his direction; but a second later Dennis drove his knife with all his force at the centre of the sleek round mass.
Next moment he was thrown sprawling on the ground, by a flick of the tail as the upper part of the serpent's body writhed convulsively under the blow. He jerked himself to his feet and leapt away through the undergrowth in panic fear. A few steps brought him to open ground, and then, crushing down his nervous terror, he looked back. The coils were slipping down the tree, and in a moment it was clear that the serpent's power was gone; its huge bulk moved uncontrollably: its motor force was destroyed. Dennis ventured to enter the thicket again. When the serpent reached the ground, it writhed as he had seen injured eels and earthworms writhe, but its movements were all involuntary; Mirandola was saved.
"Dennis saves Mirandola."
The monkey was now chattering volubly, but still clung to his perch. Clearly he would not venture to descend while his enemy moved. For some time Dennis watched it; then, feeling that he must put an end to its maimed life, he hurried away to fetch his gun. A bullet in the head: and the reptile lay motionless.