system
Given the following post, respond as if you're commenting on Reddit:
human
[LOTR] In the Two Towers film (extended), Gimli says an Uruk-hai he killed is twitching because his axe is stuck in its nervous system. Are the inner workings of the nervous system and the rest of human/elf/dwarf anatomy known in Middle Earth?

Or was this just a fun little line thrown in by Peter Jackson and company?
gpt
Everything that the characters say is translated into English for our benefit - the language that they're actually speaking is Westron.

That comes with its handful of quirks in the translation.  Like when the Uruk-Has and the Mordor orcs are fighting over whether to eat Merry and Pippin and one yells out "Looks like meat's back on the menu!"  Orcs don't know what a menu is, because orcs don't have restaurants.  At least not restaurants with any decent options.  But instead of translating it directly as "Looks like meat's back on the grub-slab" a little bit of liberty was taken with the translation.

Likewise, Gimli may not have said "nervous system," though it's not impossible that the Elves and Dwarves know a fair amount about  anatomy.   He may have just been saying something similar that got translated a little more colorfully.