As the shadows grew and the twilight deepened, the undercurrent of savagery that is the eternal quality of the wilderness grew ever more pronounced. A thrill and fever came in the air, mystery in the deepening shadows, and brighter lights into the eyes of the hunting folk. The dusk deepened between the trees; the distant trunks dimmed and faded quite away. The stars emerged. The nightwind, rising somewhere in the region of the snow banks on the highest mountains, blew down into the Killer's face and brought messages that no human being may ever receive. Then his sharp ears heard the sound of brush cracked softly as some one of the larger forest creatures came up the trail toward him. The steps drew nearer and the Killer recognized them. They were plainly the soft footfall of some member of the deer tribe, yet they were too pronounced to be the step of any of the lesser deer. The bull elk had left his bed. The red eyes of the grizzly seemed to glow as he waited. Great though the stag was, only one little blow of the massive forearm would be needed. The huge fangs would have to close down but once. The long, many-tined antlers, the sharp front hoofs would not avail him in a surprise attack such as this would be. Best of all, he was not suspecting danger. He was walking down wind, so that the pungent odor of the bear was blown away from him. The bear did not move a single telltale muscle. He scarcely breathed. And the one movement that there was was such that not even the keen ears of an elk could discern, just a curious erection of the gray hairs on his vast neck. The bull was almost within striking range now. The wicked red eyes could already discern the dimmest shadow of his outline through the thickets. But all at once he stopped, head lifting. Perhaps a grizzly bear does not have mental processes as human beings know them. Perhaps all impulse is the result of instinct alone,--instinct tuned and trained to a degree that human beings find hard to imagine. But if the bear couldn't understand the sudden halt just at the eve of his triumph, at least he felt growing anger. He knew perfectly that the elk had neither detected his odor nor heard him, and he had made no movements that the sharp eyes could detect. Just a glimpse of gray in the heavy brush would not have been enough in itself to arouse the stag's suspicions. For the lower creatures are rarely able to interpret outline alone; there must be movement too. Yet the bull was evidently alarmed. He stood immobile, one foot lifted, nostrils open, head raised. Then, the wind blowing true, the grizzly understood.