Zombies are immune to corrosive damage-over-time. Initial corrosive attacks damage them at the same rate as bare flesh.
Zombies appear in large groups, and despite being relatively slow can wreak havoc with brutal melee attacks if allowed to surround the character. Use their speed against them by cutting them down from afar, before they can overwhelm in close quarters.
Zombies that have their heads freely hanging back can be difficult to make headshots on; wait for them to attack so they expose their head, or else set them on fire. It is also possible to score critical hits on these zombies by jumping and firing at the head when at the maximum height of the jump. Recommended weapons to do this with are accurate shotguns and strong revolvers. Aim to put the head in the bottom 25-30% of the reticle for the best chance to land the hit.
Zombie's slow movement speed is equalized by their high melee damage. Always avoid close range if possible and, if cornered, use a powerful revolver or shotgun to make some space to flee.
Among a horde, Defilers should almost always be singled out first for their ability to impair your movement, thus allowing a group of zombies to catch up to you and injure you.
When Zombies are about to spew bile, they will pause briefly, and shake slightly as a sign of them about to do so. If you see a Zombie doing this, take an evasive maneuver or headshot it quickly.
They will often spawn behind the player or in multiple locations in the immediate vicinity and can catch the player off guard. Retreating to either a choke point or cleared area is highly advised once they start coming out of the ground or spawn in general. They also rarely if ever make any noise when approaching their target, only when they are pulling themselves out of the ground, dying and attacking.
Shotguns with high accuracy are useful for farming brains, as a decent shotgun can easily kill a zombie in one shot, and will generate a brain drop even if the spread only partially strikes the zombie's head.
Shooting the legs off a regular zombie makes it crawl on the ground, turning it into a Torso zombie, however, it will still be called "Zombie."
While they are simply called Zombies, they have several appearances and running styles to offer variety (i.e.: beer hats, no headwear, different clothes, different posture, arms close together or far apart, etc.). This does not affect their damage or overall health in any way.
As stated in the loading screen hints, zombies are capable of hastening a crippled player's bleed-out period by attacking a player when he is down. Fortunately, the nature of the threat (large numbers of easily killed opponents that approach to melee range) makes it easy to obtain a Second Wind. However, harder to kill zombies like tankensteins are also capable of hastening the bleed-out, making a Second Wind much harder to obtain if no weak zombies are present and alive.