Comic book spoilers! Everyone becomes a zombie after they die. That is how there are so many of them and why they are everywhere. You have to destroy the brain for them to really die.
like even people that died years ago...?
Anyone who was alive when the virus or whatever it was spread.
but, like, including someone that died of a non-zombie related heart attack...?
that'd increase the numbers of potential zombies, but not by all that much. maybe a percentage point or two. IF, however, it was black lantern like and zombified anyone whose body was still a body, even if you died years ago... that'd not only be pretty cool, it'd explain why there're so many.
