> Things we think about as "soft" can be remarkably hard at high velocity. At 120 mph terminal velocity, water and concrete are similarly fatal: the incompressibility matters more than the hardness.
And yet planes fly through clouds and rain at several hundred mph without issue, though the same wouldn't be said about flying through concrete...
The issue here is relative hardness. Bone is relatively soft to titanium turbine blades, whereas screws and titanium turbine blades are in the same ballpark of hardness, so are catastrophic when they meet when spinning @ several thousand rpm...