Moon-Watcher and his group don't remember being experimented on the next day. Not clear if that's because they've been hypnotized or because they don't generally remember stuff.
Another encounter with the Others.
And at night back to the slab. It only picks the best and the brightest to mess with this time. That includes our hero, Moon-Watcher.
It shows him visions of him and the man-apes all contented and happy and having eaten enough.
Give a man-ape a dream, and next thing you know you'll have a moon rocket.
The slab keeps showing him the contented man-apes over and over in their little four person family grouping. Why just two little man-apes in this domestic scene? Maybe because in Arthur C. Clarke's day, two was a reasonable number of kids.
It says that the new patterns of Moon-Watcher's brain would be passed on to his kids through his genes. So the slab is rewriting his genes, supposedly. Tricky slab.
But not tricky enough; during one night, it accidentally fries the brain of a man-ape. Dead man-ape.
The slab goes dark for one night, but then it goes on as before. Moon-Watcher is seeing terrible, wonderful visions of man-ape life to come.
One day, Moon-Watcher sees a pig, and inspired by his time with the slab, he picks up a rock, and then he kills the pig.
He thinks he will never be hungry again, like Scarlett O'Hara, but more Neanderthalish.