A friend is a neurosurgeon and they use some special saw that stops as soon as there's no hard tissue providing resistance. So you press it hard into the skull, and when it's done chewing through the bone, it immediately stops.
Apparently the scariest bit for the junior doctors to learn to use, somehow.
Same or very similar stuff is used to cut plaster casts for broken bones. You see that small circle rotating next to your veins in legs and there is suddenly some tension in the room. Especially when saw seems to keep stopping when cutting through plaster for no good reason, causing some confusion for the doctor and making him lean more heavily into it.
Afterwards they realize that harder resin casing was layered with soft fabric by previous orthopedic surgeon in previous hospital, so the thing actually worked as intended (but if you keep pressing power button and leaning into it it will keep cutting). Talking about hospital equipment in Switzerland, 2 weeks ago after a nasty paraglider crash landing.
edit: though actually I googled the skull saws which I wasn't familiar with and they might work on a similar principle, found someone talking about using them in autopsies anyway.
That's strange. Cast saws don't need to stop like that; they can't cut skin even running at full speed. Your grey matter is not as tough as your skin and you wouldn't want to touch it with even a gentle power tool, though, so it makes sense that brain-surgery saws would be different.
I'm forever grateful to the doc who actually pressed the running sawblade into his hand to prove that it's harmless, instead of just saying "don't worry, it's safe" while going to town on my leg with a power tool.
Apparently the scariest bit for the junior doctors to learn to use, somehow.