Another man-ape came to life, and went through the same routine. This was a younger, more adaptable specimen; it succeeded where the older one had failed. On the planet Earth, the first crude knot had been tied.

Others did stranger and still more pointless things. Some held their hands out at arm's length, and tried to touch their fingertips together – first with both eyes open, then with one closed. Some were made to stare at ruled patterns in the crystal, which became more and more finely divided until the lines had merged into a gray blur. And all heard single pure sounds, of varying pitch, that swiftly sank below the level of hearing.

When Moon-Watcher's turn came, he felt very little fear. His main sensation was a dull resentment, as his muscles twitched and his limbs moved at commands that were not wholly his own. Without knowing why, he bent down and picked up a small stone. When he straightened up, he saw that there was a new image in the crystal slab.

The grids and the moving, dancing patterns had gone. Instead, there was a series of concentric circles, surrounding a small black disk. Obeying the silent orders in his brain, he pitched the stone with a clumsy, overarm throw. It missed the target by several feet.

Try again, said the command. He searched around until he had found another pebble. This time it hit the slab with a ringing, bell-like tone. He was still a long way off, but his aim was improving. At the fourth attempt, he was only inches from the central bull's-eye. A feeling of indescribable pleasure, almost sexual in its intensity, flooded his mind. Then the control relaxed; he felt no impulse to do anything, except to stand and wait.

One by one, every member of the tribe was briefly possessed. Some succeeded, but most failed at the tasks they had been set, and all were appropriately rewarded by spasms of pleasure or of pain.