Zombie Lore:

The walking dead are the creations of necromantic ritual and are, generally speaking, more like automatons than thinking beings. There are a few stories of zombies recognizing a loved one or demonstrating a phobia held in life, but these are more bards' stories than reliable accounts. Zombies are the most common type of mobile corpse, and will last up to 20 years before wearing out.

The zombie will follow all of its master's instructions to the best of its limited intellectual ability. A zombie may also be given a set of instructions and conditions to follow when it is animated, and thus may be given a limited measure of autonomy. Zombies are notoriously stupid, but will do as instructed, or at least they will attempt to do so. The corpse to be reanimated must be reasonably intact—poison victims are the best, certain diseases are second—and must have died no less than approximately three days (72 hours). Remember that zombies are rather dim, & could easily become confused & overwhelmed by complex or conflicting instructions.