Yeah, I understand what you're saying, but from a simplistic standpoint, with the human body being 80% water, wouldn't it hold to reason that a Water-Bender could pull/bend that "water"? Regardless of the Water-Benders predilection for Blood-Bending..Ysmir said:The reason why it's a tough skill to learn is your not only bending their blood. You are thinking of it too literally, you are overpowering their will, which makes it extremely hard skill to pick up. It's not just about manipulation of the blood it is bending their body, their will. The creators and even in the cartoon hint at this. If anything, in Legend of Korra they made it "easier" to Blood-bend as shown when they easily would Blood-bend each other or that pack of Wolves. Of course you have people like Noatak/Amon who were so adept at it they could manipulate people's chakras to the point it removed their bending.
Unless there is some hidden unmentioned "chakra flow" entrinsic to all humans, be they Benders or mundane, that prevents anything within their body from being manipulated by Bending. Which would thus limit the extent of Blood-Bending, and reduce it to mere overpowering of will. Sort of like a reverse resonance of internal chakra that nullifies internal bending.. *shrug*