"Береги свою голову, там мозги"

In English, when it comes to fancy sayings, usually "head" is already used to mean "brains" or "mind" by extension, so when I first read it, I hit a bit of a wall too. I read the first half already thinking of the mind, so then the second half didn't seem as if it was adding anything. "Protect your mind, that's where your.... 'brain matter' is?...Uh... Well sure I guess..."

That's a super interesting difference!