Moon-Watcher gets woken up by the sound of metal across stone. Which he doesn't recognize, since the man-apes haven't even figured out stone tools, much less metal ones.
The tribe goes down to the river and they find the New Rock. It shakes its hips and says, "Love Me Tender."
Okay, it's not the Elvis kind of New Rock. It's a big transparent rectangular slab kind of New Rock.
Moon-Watcher decides that it's a rock that has grown during the night. (The novel thinks Moon-Watcher is cute. Shmoop feels like maybe the novel shouldn't be so condescending. Respect the man-apes, Arthur C.)
Since Moon-Watcher thinks it's a plant, he tries to eat it. That doesn't work.
So he forgets about it.
He shrieks at the Others.
Moon-Watcher's tribe goes to forage, and they don't find much. One female collapses, and they have to leave her, since they don't have energy to drag her along.
There are drums. There are lights. There is…Elvis! (Okay, still not that kind of New Rock.)
The slab is evaluating them and figuring out what to do with them.
The man-ape nearest the slab moves around like a puppet; he picks up a couple of grass stalks and moves to knot them together, but he can't do it.
A second man-ape does the same thing, but this time he manages the knot.
Way to go, man-ape! Way to go, big slab! Together, ye shall knot the world! (Fanfare here.)
Anyway, other man-apes do various things.
Moon-Watcher's turn comes, and the slab gets him to chuck a stone at the slab. When he gets a successful hit, he feels almost sexual pleasure.
This is as close as the book gets to a sex scene, by the way. (See Steaminess Rating.)
Every man-ape gets its turn, and finally the slab lets them go back to their caves.