Zombies have many methods to terrorize its adeversaries.
The most notorious and deadly methods of attack, a single bite can lay waste to even the most robust foes. Against animal adversaries, a single bite will slowly kill the animal like poison. Against a human adversary, a bite will allow the zombie to spread its virus to the bitten victim. This causes massive problems in a group.
The second method of attack, scratching is a secondary attack used by the undead. Scratching is not half as damaging as biting, but is still extremely dangerous. A zombie will scratch a target if the target is in arm's reach but not in range for a bite. A single scratch is enough to cut open a wound, allowing zombified blood to pour in if left uncontrolled. If a victim is scratched too many times, they can die by blood loss, but this is rare.
A third method of attack is moaning. The moans of a zombie does not damage an enemy in any way physically. However, it physchologically deteriorates an enemy by slowly making them depressed, and eventually insane until the enemy commits suicide or finds a way around the moaning.
Also, moaning can be seen as a call for reinforcements, because other undead will hear the moan and investigate its source. Luckily, this can be used to your advantage if an undead is moaning from somewhere far away from base.
Unlike the other two attacks above, moaning is not done intentionally, but done reflexively when an undead spots a prey. If a moan is heard, one should know that an undead is already aware of his or her presence.
A fourth method of attack is bashing. This is done when an enemy undead simply swings its arms at a high speed toward the direction of a prey. The direct damage done to a prey by bashing is fairly low, causing only moderate pain and a bruise at worst.
Probably one of the least recognized methods of attack, bleeding is still a devastating counterattack if overlooked. A bleeding undead is relatively harmless against a foe if there are no open cuts. However, if there is an open cut, the undead blood may pour into the cut and infect the foe. Also, blood splatter can go into the eyes, nose, or mouth and can kill/infect an enemy that way.
The only true way to defend oneself against bleeding is to wear goggles, gloves, and thick clothes at all times. It is also recommended to put a waterproof bandage on any wound there is to prevent blood from soaking in.
An undead grab is a devastating method of attack that is used in combination to biting. For the most part, grabbing is relatively harmless unless the undead has long fingernails and digs into your skin. However, the undead is likely to follow up with a bite or a scratch, and depending on how strong an undead is, this can mean doom.
The only true way to counter grabbing is to carry a small melee weapon or a handgun that can be used in arms reach without much of a problem.
Like bleeding, decomposing is a counter-attack for a defeated undead. A poorly handled corpse can cause infection if an undead wound brushes a survivor's wound. On top of that, a dead undead will decompose and will become a health hazard in a matter of days.