The reanimated pathogenic-vectors (i.e. zombies) are the non-human antagonists in State of Decay. It isn't known what exactly created them, but it is assumably pandemic-related (due to the description of the Hazmat hero). The majority of the zombies varies widely across the decomposition spectrum and their behavior equally varies (sloths, walkers, runners, etc.). Some become mutated, taking distinctive appearances and characteristics; these special zombies are known as "Freaks".
The most efficient ways to kill the undead is to destroy the brain, whether it's bashing it in with a baseball bat or shooting them from a distance with a rifle. When their limbs are dismembered via edged weapons or gunfire, Zeds will ignore the pain and continue trudging towards the survivors, making dealing with the head the only realistic option to kill Zeds on foot.
When Zeds are repeatedly attacked (but not shot in the head), they may stumble and fall on their knees, or fall face down, making them vulnerable to execution attacks. However, if they are not dealt with quickly when they are most vulnerable, Zeds would quickly get back up again to chase the survivors.
Occasionally, a large number of zombies will gather in a random location, creating an Infestation.
"Hordes" are herds consisting of 10-20 zombies that travel together as a hive-minded undead unit. These are extremely dangerous for both the player and the other survivors in Trumbull Valley.
In State of Decay a number of special zombie subtypes exist. Often called "Freaks", these zombies possess unique properties that regular zombies don't have.
Due to the stealth system in place in SoD, zombies rely on an "aggro system" to detect a survivor and/or playable character. Several functions affect detection. Such as line of sight, sound, lighting, movement and whether or not there is the presence of a player used distraction. Smell will not be taken into account in detection.
In larger affect is a Horde system, over time, base and outpost activity will cause zombies to spawn in the region around the base, if the problem is not dealt with, such as clearing out infestations, a horde will attack the base and attempt to destroy it.
To reduce lag and processes in the game, depending on the distance different animations and AI will take place, zombies beyond/out of player sight will have very simple AI with movement and detection in place. As the player comes into sight the AI will become more advanced, with a more advanced detection and movement system. Once in combat range of a player, the AI will be in its most advanced form, with all mechanics and animations in place.