Poison Zombies are unique in the fact that the Headcrabs attached to their bodies appear to be interacting with their host. They also emit loud, whale-like howls when taking damage. Poison Zombies can be detected by their loud, strangulated breathing and muffled groans. Poison Zombies themselves are not poisonous but rather rely on the hitch-hiking poison headcrabs to attack first. Poison Zombies can take three times as much damage as other zombies before collapsing. The Poison Headcrabs riding on the Zombie's back can leap off when needed in order to attack on their own, but cannot, or will not reattach themselves to the Poison Zombie once left.ДЄnother trait that distinguishes the Poison Zombie from other zombie types is its endurance. It appears that the Poison Zombie's model is an old man's, but its stooped posture and shuffling gait could also be caused by the weight of the attached headcrabs, or (as seen by the exposed spinal column) because it's missing all the supportive muscles from its back which would allow it to pull the upper torso into an upright standing position. They are almost always seen carrying three additional Poison Headcrabs on their back. Poison Zombies are bloated, reddish purple, slow-moving zombies.

Half life 2 sounds