Yeah, fractured ceramics can be more than sharp enough - really metal is a downgrade at the microscopic level. The trick is that it's pretty hard to get a totally straight edge. The Aztecs did it, but it sounds like it required a mass-produced supply chain of some unknown kind (and I'm not even sure if grinding has been ruled out).

I miss a strip on on my non-dominant side every once in a while using power clippers, and we're talking about a wiggly little stone scraper. Primitive people spend all that time we spend on books working with their hands and body instead, and would have a ton of family around, so they'd probably never have to do themselves, but it's still kind of impressive.