Jokes are hard.

> Torturers don't hit people in the head

The comic doesn't say hit the person in the head, it says "hit him with this $5 wrench", and did not specify what to hit.

https://xkcd.com/538/

A sophisticated in-depth treatise on torture wouldn't fit neatly into a 2 panel webcomic. If you email Randall, maybe he'll make a comic just about torture for you, but either way, the $5 wrench gets the meaning across well enough. Personally, I haven't given much thought on how to torture someone into giving me information they don't want to tell but I'm grateful someone's done that work, hopefully on the side of good and not evil.

The XKCD comic just said hit them, not necessarily in the head. Personally, I know I wouldn't last ten seconds with a pair of broken kneecaps.