Charlie: A zombie is a creature without a brain that still walks around. We think of them as humans, but any creature can have its brain eaten by zombies and become a zombie.
Except for--wait, what are those creatures that look like sea cactus, only they don't have any spines or bear any cactus fruit? They camouflage and can become any color when they wish to hde from predators?
Charlie: That is cowwect. Ana. Anana. An enomy cannot become a zombie because it does not have a brain! So how could a zombie eat its brain to also turn I into a zombie? So a zombie is a creature that used to have a brain that doesn't anymore but still walks around.
Way to narrow your definition down to something more accurate, chuckster.