I think you're right, blackstar. Although the zombies only shuffle around, they can do so indefinitely--walking is one of the most efficient forms of locomotion. While the rest of us run around like maniacs trying to get away, we are expending massive amounts of energy and will eventually need rest. Meanwhile, the zombies continue their inevitable progression towards us. Literally, they are walking us to death.
"Nothin' up my sleeve. . ." --Bullwinkle J. Moose