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.