Here's how he told the story of that scene to Justin Bozung, author of a long and extremely interesting interview with the apeman we know as Moonwatcher.
"It took us weeks to do that scene. The page of the script said something like, “Moon-Watcher picks up a bone, he now has the power..and he will kill” or what not. All Stanley told me was, “Go over there and pick up the bone. Hit the skull and break it.” That’s all he told me!"
"The whole film was shot on a sound stage, except the end of that scene. We did it outside of the studio. In fact, there were buses driving behind me as we were doing it. So I’m sitting there on this platform up in the air and I’m looking out at the camera, and I noticed the type of lens Stanley was shooting with and the angle in which I was being filmed. I noticed he was shooting with a portrait lens. And I knew we were shooting in Cinerama. So I knew that I was going to be gigantic on the screen. I had to show visually that “Moon-Watcher” had this idea that was put into his head by these aliens. I had to show that somehow.
So I thought about it. Then I thought it would be good if I just cocked my head slightly. So I had to protect the entire moment by not doing much. I decided to move very slowly forward, and look very carefully down at the bones. I wanted to make it so that it filled the screen, so that the moment where I cocked my head would signify this change in the script, like a beat."
"In fact, the whole time I was doing that scene, I was talking to Stanley through the mask. We’re shooting it “MOS” (mitt-out sound, meaning that a film segment has no synchronous audio track; the sound for The Dawn of Men was recorded later in post-production), so I was saying to Stanley “OK, I’m going to move to the left a bit”, and Stanley would say, “OK, that’s good. Just reach over.”
So, when it came time to pick the bone up, I was playing with the idea of hitting things, because remember he had never picked anything up before, never held anything in his hands, never knew how to wrap his hand around anything. Everything was totally new to him. I took the time to feel the weight of it in my hand. Then I started probing things with it. Then at that moment, I hit one of the little bones, and it spun up into the air. I said to Stanley, “Oh, I screwed up Stanley.” He said, “No, no I like it keep going.” So we started to grow the scene from that. We set it up again, so that all of the bones would flip into the air as I hit them."
And here's a short excerpt from Dan Richter's excellent book Moonwatcher's Memoir:
"He feels it, smells it and lets it fall against the other bones. He begins to sense the weight in his hand, the power, the release from an eternity of fear and groveling in the dirt for food.
"I let Moonwatcher play with the bones. He gets the feel of a bone in his hand. He has never held a bone in his hand before; he has never used a weapon. This is not only the first time for him, but it is the first time any creature has ever picked up a weapon."
"Action."
"I give it all I have as I move forward into film history."
"I give it all I have as I move forward into film history."