And—as she kept being reminded—they were inherently unstable. As long as she remained on areas of larger rocks, her weight was not sufficient to break anything loose, but when she strayed into sandy or gravely areas she set off little avalanches. Nothing big enough to be dangerous, either to her or (unfortunately) those below her, but enough to give her the impression that she was climbing on a treadmill, burning energy but, like Sisyphus, going nowhere.