As time went on and month followed month, Robin found himself working into a comfortable, if primitive, routine. He charted exactly what to do on what days. He could tell in advance what he would be eating, what he would be harvesting. His rabbits had become sufficient in number to permit slaughtering, and he began to acquire a pile of rabbit furs. He found it no longer possible to keep all his rabbits in one pen, and finally liberated the majority of them and left them to shift for themselves. This worked out fine, and he never lacked the sight of at least one or two bunnies anywhere he looked. During the two weeks of winter each month they simply holed up as they might have done on Earth. It was an odd sight seeing the rabbits run wild, for their powerful leg muscles were many times stronger than was required by the weak gravity and, when they ran in a hurry, they would bounce many feet high in fantastic leaps. Robin was now wearing a rabbit-fur outfit of coat, pants, and hat during the winter periods, equipped with bone buttons he'd carved from the Moonhound skeletons. He was, if anything, beginning to gain weight, but he was also aware of the paleness of his skin. He wondered whether staying in this sunless world a sufficient number of years would not make him as palely transparent as the Moonhounds. But all this time Robin had not forgotten his ultimate mission--to reach the surface and signal for help. He had worked out the problem in his own mind. He had to make some sort of space suit, something that would permit him to venture out on the nearly airless surface long enough to set up a signal that astronomers might see. He knew he had the materials for part of this suit in the metal salvaged from the rocket nose. He could polish a section sufficiently to make a heliograph with which he could flash a code message to any high-powered telescope that might be pointed his way. But he had also to fashion the metal into an airtight space helmet, and that he did not know how to do. The suit itself he could probably fashion from cloth and tanned skins, sew and seal it tight enough with animal fats and bone glue to be airtight for a short period, but he needed the helmet. He had the glass for it too, the little peepholes for the camera outlets and a large circular plate that had been set in the very base of the cargo nose and evidently intended for a wide-vision camera shot of the Earth. This plate would be his face plate. Robin was aware of the hissing noise that he had first noticed on his arrival, but he had never investigated it. It was far off, somewhere along the wall of the cavern. One work period, when he found himself ahead of schedule, he set out to find the source of the noise. Following the wall, with Cheeky running ahead chattering, the hiss gradually grew in volume. Robin made his way over a sharp cleft, skirted a large bubble-cave in the wall, and after about two miles of walking, came upon the source.