I've been shot in the arse by an arrow that previously had been in a zombie's brain....
I think it's conclusive proof that Zombieism isn't an infectious disease, but the result of poor lifestyle choices, or possibly hereditary.
Or, if I have, I don't remember.
Maybe the infection is passed on through Zombie saliva, which just happens to get into your blood when they bite you. Or maybe the bottom is impervious to zombie-ism. What happens if a zombie bites you on the arse?