It was a rectangular slab, three times his height but narrow enough to span with his arms, and it was made of some completely transparent material; indeed, it was not easy to see except when the rising sun glinted on its edges. As Moon-Watcher had never encountered ice, or even crystal-clear water, there were no natural objects to which he could compare this apparition. It was certainly rather attractive, and though he was wisely cautious of most new things, he did not hesitate for long before sidling up to it. As nothing happened, he put out his hand, and felt a cold, hard surface.

After several minutes of intense thought, he arrived at a brilliant explanation. It was a rock, of course, and it must have grown during the night. There were many plants that did this – white, pulpy things shaped like pebbles, that seemed to shoot up during the hours of darkness. It was true that they were small and round, whereas this was large and sharp-edged; but greater and later philosophers than Moon-Watcher would be prepared to overlook equally striking exceptions to their theories.

This really superb piece of abstract thinking led Moon-Watcher, after only three or four minutes, to a deduction which he immediately put to the test. The white round pebble-plants were very tasty (though there were a few that produced violent illness); perhaps this tall one...?

A few licks and attempted nibbles quickly disillusioned him. There was no nourishment here; so like a sensible man-ape, he continued on his way to the river and forgot all about the crystalline monolith, during the daily routine of shrieking at the Others.

The foraging today was very bad, and the tribe had to travel several miles from the caves to find any food at all. During the merciless heat of noon one of the frailer females collapsed, far from any possible shelter. Her companions gathered round her, twittering and meeping sympathetically, but there was nothing that anyone could do. If they had been less exhausted they might have carried her with them, but there was no surplus energy for such acts of kindness. She had to be left behind, to recover or not with her own resources. They passed the spot on the homeward trek that evening; there was not a bone to be seen.