"I didn't hear anything," said Gilbert. "Nor I," added Warley. "But my hearing is not nearly as good as Frank's. I've often noticed that." "Let us stop and listen," suggested Charles. They all stood still, intently listening. Presently a faint sound was wafted to them, apparently from a great distance--from the edge of the sandy desert, they fancied, which was still visible beyond the wooded tracts. "No," said Charles, when the sound had been twice repeated, "that is not the cry of any animal, with which I am acquainted. It sounds more like a human voice than anything else. If it was at all likely that there was any other party of travellers in these parts, I should think they were hailing us. But nothing can be more improbable than that." "Still it is possible," urged Warley, "and they may be in want of our help. Ought we not to go and find out the truth?" "I think you are right, Ernest," said Frank. "Well, I don't know," urged Gilbert, nervously. "I've heard all sorts of stories of voices being heard in the deserts, enticing people to their destruction, and it may be some ruse of the savages about here, who want to get us into their hands, to possess themselves of our guns. What do you say, doctor?" "Why, as for the voices, Nick, I've heard the stories you speak of, which have been told chiefly by persons who had lost their way and were nearly dead from cold and hunger. Under such circumstances, when people's nerves and senses begin to fail them, they fancy all sorts of strange things. No doubt, too, there are all sorts of acoustic deceptions in these wild regions, as there are optical delusions; but I don't think we four--all of us in sound health--are likely to be so deceived--" "But how about the savages, doctor?" interposed Nick, anxiously. "Well, if these were the backwoods of America, and we had the Red Indians to deal with, there would be a good deal in your suggestion. But neither the Hottentots nor the Bushmen are given to stratagems of this kind. However, we'll move warily, and if any treachery is designed, we shall be pretty sure to baffle it." They turned off in the direction whence the cry had come, keeping to the open ground, and giving a wide berth to any clump of trees or underwood which might harbour an enemy. Every now and then they paused to listen for the sound, which was regularly repeated, at intervals apparently of two or three minutes, and grew more distinct as they advanced. It was now certain that the cry was human, and sounded like that of a full-grown man. "We are getting a good deal nearer," observed Warley, as they passed the last patch of trees, and entered once more the sandy wilderness. "I should say we must be almost close, only I don't see any place where the person who is crying out in this manner can be hidden." "It comes from that heap of stones there," exclaimed Frank, "that heap to the left, I mean--about two hundred yards further on."