"What am I waiting for?" he asked himself, half aloud. The monkey stopped at the sound of his voice, looked at him. Robin had developed the habit of talking to himself. He was aware of the danger that years of this hermit's life might well cause him to forget how to talk, and he did not want that. "I can't use a space suit until I can find a way to the surface--a safe way. And I've never even really explored this cavern itself. Maybe there's a simpler way of communication with the surface." He sat and thought. The monkey dashed over to him, jumped on his knee, chattering. "I really ought to get about exploring this place," Robin went on. "You know, Cheeky, there might be some more things we can use. What do you say, shall we spend this next week playing Columbus, looking for more bubble worlds to conquer?" The monkey chattered happily, jumped off his knee, and ran around. "Guess you like the idea," said Robin. "Let's get about it, then." He got up and made his preparations. He filled a sack with enough food for several days. He took his homemade canteen, made from a hollowed-out Moontree fruit rind, filled it with water and hung it around his neck. He took his flashlight and knife, his bow and arrow, and his lantern of light organs. He had discovered that the little light-giving bulbs the animals carried would glow for about two days after their removal, and therefore he constantly kept this lantern refilled with his latest catches. He looked to see whether his special lot of penned rabbits had enough food and water for the period and then, whistling to Cheeky, Robin set out. He went down to the bank of the flowing stream on which he had been originally carried and then set out to follow this rivulet its length into the distances of the bubble-world. He followed the flowing stream for about twelve miles. The bubble widened out and the water, which had originally brushed the other side of the cavern where Robin had lived, had now narrowed as a bank of dry ground formed on the opposite side. Robin found himself walking through an ever deepening thicket of growing Moontrees which went on for many miles. The stream twisted and moved off at right angles finally rushing into a deep pool. Robin went over and gazed into it. Plainly the pool had some sort of underground opening, for the water was swirling around with no visible surface outlet. So this was where the stream ran to! Doubtless it emptied into another bubble somewhere below, probably to fall like a waterfall into that space, there to become another stream and empty still again farther down until it ended in some vast reservoir of sublunar seas. But Robin was not interested in going farther down, he sought a way upward toward the surface, toward the sight of Earth. He turned away from the whirlpool, walked boundingly on to the farther wall of his home-bubble. He reached it in time for his sleep period. It seemed as solid and impregnable as the wall around his home region.