He halted and turned his head like lightning, grasping his rifle in his nervous, determined way as he peered back into the gloom, whispering to himself: "That must be Lone Wolf or some of the warriors coming back to look for me." This was rather vague theorizing, however.

Look and stare as much as he chose, he could detect nothing that resembled man or animal.

He shrank to one side and waited several minutes, in the hope that the thing would explain itself.

But it did not, and, after waiting some time, he resumed his journey along the ravine, keeping close to the shadow on the right side, and using eyes and ears to guard against the insidious approach of any kind of foe.
Sometimes, under such circumstances, when a sound has very nearly or quite died out In the stillness, there seems to come a peculiar eddy or turn of wind, or that which causes the sound, passes for an instant at a point which is so situated as to impel the waves of air directly to the ear of the listener.

Fred did not exactly understand how this thing could happen, but he had known of something of the kind, and he was gradually bringing himself to explain the thing in that fashion, when his theory was upset by such a sudden, violent rattling of hoofs, so close behind him, that he leaped to one side, fearful of being trampled upon.
"That's a pretty way to come upon a fellow!" he gasped, whirling about with the purpose of shooting the red-skin for his startling introduction.
But neither rider nor horseman was visible.
The watcher could scarcely believe the evidence of his own senses.
It seemed to him that the Apache, as he believed him to be, must have turned abruptly aside, into some opening in the side of the ravine, but he could not remember having seen any place that would admit of such strategy.