The robot’s operators had to think fast. Should they follow the native or find out what it had been doing up the hill? The former might seem more logical, since the native was leaving, and the hill presumably was not, but the second alternative was the one they chose. After all, it was impossible for the thing to travel without leaving some sort of trail; besides, night was approaching, so it wouldn’t get far. It seemed safe to assume that it shared the characteristic of Tenebra’s other animal life, of collapsing into helplessness a few hours after nightfall.

Besides, looking at the hilltop shouldn’t take too long. The robot waited until the native was well out of sight, and then moved up the hill toward the gully. This, it turned out, led into a shallow crater, though the hill bore no resemblance to a volcano; on the crater floor lay perhaps a hundred ellipsoids similar to that which the native had just left there. They were arranged with great care in a single line, and except for that fact were the closest things to loose stones that the men had yet seen on Tene-bra. Their actual nature seemed so obvious that no effort was made to dissect one.

At this point there must have been a lengthy and lively discussion. The robot did nothing for quite a long time. Then it left the crater and went down the hill, picked its way carefully out through the “mine field” on the trail of the native, and settled down to travel.

This was not quite as easy as it would have been in the day time, since it was starting to rain and visibility was frequently obstructed by the drops. The men had not yet really decided whether it was better, hi traveling at night, to follow valleys and remain submerged or stick to ridges and hilltops so as to see occasionally; but hi this case the problem was irrelevant. The native had apparently ignored the question, and settled for something as close to a straight line as it could manage. The trail ran for some ten miles, and ended at a clearing before a cave-studded cliff.