The slab is gone; Moon-Watcher and the others don't even know it's gone.
Again, they seem like they're dumber than house pets. If you put a giant slab in the living room for several years, and took it out, a freaking cat would notice. But hey, maybe ancient man-apes really were this, er, simplistic.
There are the Others on the other side of the stream again.
But this time instead of challenging and squawking back, Moon-Watcher and the tribe go to the other side.
Moon-Watcher has a stick with the leopard's skull on it.
Most of the Others run.
One-Ear, the leader of the Others, doesn't run, so Moon-Watcher beats him to death with his club.
Now Moon-Watcher is master of the world. Which seems like it's supposed to be a cool achievement, though what One-Ear did to deserve being clubbed to death is not especially clear.