They set out accordingly, following without difficulty, by the help of the moon, the course taken by the herd across the open plain and the intervening patches of scrub for two or three hours. The marks of blood were plainly enough visible all the way, sometimes in large patches, as though the wounded animal had stopped behind the rest through momentary weakness; and then again only a drop here and there, as if it had again exerted its remaining strength to overtake the herd. At last they came to a spot where a larger puddle than any before stained the adjacent grass and sand, and then the marks no longer followed the general track, but turned aside into a deep thicket, through which the two boys had considerable difficulty in following its course. They had advanced some distance, when Nick suddenly laid his hand on his companion's arm. "Did you hear that?" he said. "Hear what?" returned Wilmore. "I fancied I heard a shot fired," said Gilbert, "but I suppose I must have been mistaken." "A shot! Who could there be in these parts to fire one? It was the fall of a large stone from the cliffs, most likely. They are often dislodged by the wind, and make a noise like the report of a gun. Come along, we shall not have much further to go, I expect." "Hist!" exclaimed Nick, again stopping. "I am quite sure I hear something now, though in a different quarter from that in which I fancied the gun was fired." "What do you hear?" asked Wilmore, stopping and listening with all his ears. "A kind of low growling, or groaning," answered Nick; "or perhaps grinding of teeth. It is very indistinct; but I am certain that I hear it." "It is the poor brute in his dying agony," said Frank. "Push on. We must be close to him now." By this time the dawn had begun to break, and the daylight diffused itself rapidly over the scene. The beams of the rising sun showed that they were, as Frank said, close on the buffalo's trail. The grass was trampled down, as if by heavy footsteps, and blood, evidently only recently shed, stained the bushes and long grass in profusion. And now the sound heard by Nick became plainly audible to Frank also. "Cock your gun, Nick!" he said. "He may have life enough left in him to give us some trouble yet." As he spoke he turned the corner of a large mass of prickly pear, which had been partly forced aside and partly torn away by the passage of some heavy body, and came upon a sight which was as alarming as it was unexpected.