It was not anything he heard which gave him his first thrill of fear. He caught no sound, but it suddenly occurred to him that there was a movement in the grass a few rods out. At first he could not define its nature. It was as if some reptile, possibly a rattlesnake, was stirring at that point. The disturbance was so slight that a moment later he felt sure he had been deceived. The face of the moon cleared, and a silver flood of light bathed the grassy plain. The spot which had roused his suspicion stood out almost as at midday, when the sky is partly cloudy.