[Stingy Jack]

I always thought that zombies didn't need to see you in order to know you were there for the eating. I have seen several scenes from films where zombies have been involved in some activity (like eating a corpse, or taking a dump), and a live human being entered the vicinity. The zombies would stop what they were doing, and slowly get up and shuffle towards the living. Almost as if they "sensed" the living through some other means than sight. This would also explain how all the zombies knew there were people in the farmhouse in NOLD, and that there were people in the mall in DOTD.

Also, in the original folklore, a zombie could be stopped with salt.