It must not see the blade.

and the handle also went in after the blade and the fat closed on the blade, for he didn't draw the sword out of his body and it came out behind.

And the haft also went in after the blade and the fat closed upon the blade, so that he could not draw the dagger out of his belly and the dirt came out.

But if we look at the fossil record, we see that they made the same hand axe over and over and over again for one million years.

Now if we make some guesses about how long Homo erectus lived, what their generation time was, that's about 40,000 generations of parents to offspring, and other individuals watching, in which that hand axe didn't change.