Quote Originally Posted by DarthEnderX View Post
The other possibility is that it's also Nature chakra. We already know they draw the material that makes up their bodies from the enviroment around them. Maybe that's where the chakra comes from as well.
There's no way the ninja world wouldn't use nature chakra a lot more if it was that convenient and easy (so that even zombies can use it).

I'll just keep myself happy by imagining it's either the god of death lending power in exchange for a zombie apocalypse the foolish humans never saw coming in their greed, or Kabuto will spend his afterlife tormented by undead demons for an eternity as the high price. After all, nothing is free even if the price isn't readily apparent.