I never got that. If you get bit or eaten by a zombie you turn into one.* If you get zombie blood and guts on your open wounds wouldn't that also turn you into one? So wouldn't you be careful about all the splatter?
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* I know they changed that, but for simplicity's sake, that's how I think of it.
In the show, everyone is infected with the “zombie virus” and will turn into a zombie automatically upon death, regardless of cause.
Best I can tell you become a zombie when you die. The walker virus is not transmittable by a bite, it is simply inherent to every living human being with air being the vector. The damage from Zombie bites is that they haven’t seen Crest or Ivory Soap in a long time making the bacteria in their mouths virulent. Hence, amputate or die and when you die you Zombie up. At least that is my understanding from watching the show. :-}