Well, I get your position, such little things don't bother you; but I don't think you see what I mean with "internal consistency". There's no need for "universal biology atlas for zombies" if TFP themselves have created a system with, in essence, bad logic. You know:
1) zombies bleed from their arms when you wound them.
2) zombies don't bleed from their arms if you cause the largest wound possible, detaching the arm.
and, albeit really rare
3) if you first cause the zombie to bleed from an arm, and you then detach said arm entirely, the zombie will keep bleeding "from the arm". (This would then conflict with Roland's decent attempt, and with step 2)
What is taken from the external world, is the basic ideas of "bleeding" and "circulation" and "limbs". No need for zombie atlases. The end result is inconsistent in itself with how bleeding works, until someone comes up with an explanation and inserts it into the game. Preferably in a way that appears in several places in the game - that reinforces the made-up rule in the mind of the player and makes it more, acceptable for lack of a better word.
Does this little case matter? Not as much as I have spent time on it. How would I change it? I dunno, taking into account that the Pimps seems to have re-purposed the existing animals-only bleed effect to differentiate Blades from other weapon types, I'd say poisons would be another classic way for similar damage. Zombie poison? Why not, make the recipe use some antibiotics...

That would also solve the more generic trope of "undead don't bleed", although of course, they're usually quite poison resistant as well... but I might buy a zombie poison in a world where they've clearly learned to manage the infection somehow as the Duke is stuffing these semi-corpses into every closet in the world ...
EDIT, Woot woot! 500th post