If it was honed finely enough, could you cut yourself on a square (90 degrees) angle?
Yes.
I’ve cut myself on a machined block of aluminum, but there may have been some microscopic edge roughness.
Hit a wall or floor hard enough, and you can cut yourself on a 180 degree edge.
I tried to cut myself with a carbide scoring knife thingy. I’m not sure what it’s actually called. It’s a long rectangular prism of black metal that I use to scratch sealed NMR tubes so I can snap their tops off.
Anyway, I tried to cut myself but it didn’t work. Maybe if I really sliced hard, but I don’t actually want to bleed so I won’t try again.
ETA it’s a 90 degree edge
You can cut yourself on a piece of broken glass, and if it’s not 90 degrees, it’s pretty close.
I cut my finger open on the button on a switch-blade comb when I was a kid. Figure that one out.
People slice themselves open all the time on the corners of bricks steps etc. I sliced my foot up bigtime where my toes and feet join by running barefoot and missing a step hitting it on the exposed 90 degree brick edge of my front steps.
Cutting ability on skin is a function of force applied, acuteness of edge angle, and microscopic roughness of the edge. More of any one will offset less of the others.
As the edge angle approaches 180 degrees (ie a flat surface), the failure mode of skin at macro scale becomes more stretch until it tears than cut. But at a microscopic level it’s kinda hard to tell cut from tear.
Me too, on engine blocks.