A couple of points about the axes mentioned.
We used to heat an axe before using it in cold weather to avoid it chipping. The steel takes a lot of stress when chopping and if it is hard enough to hold an edge it can become brittle when cold.(not red hot, just warm to touch)

Bones (beef) will often chip an axe edge because they are so hard and grab the steel.

The knots in hemlock are the worst though.
Hemlock knots take out nice half moon shaped chips.
I am not sure why knots in hemlock are so bad but they are, especially the thin pin knots.

The way these bones and hemlock knots take the chip out is a bit interesting.
They don't dent or bend the steel. It isn't like what you see if you hit a nail or a stone.
It is more like they grab it and pull the chip out of the edge.
When you look at the cut the chip is still right in there. If you dig it out it is still sharp and shows no noticeable deformation.
It really is like it was simply plucked out of the edge of the axe.

I have had chips taken out of the edge of a decent machete when trimming branches off hemlocks too.
It was the knot in the centre of the branch as it entered the trunk that did that. Again, nice little crescent shaped notches neatly removed from the edge, about the size of a fingernail.