Headcrab Zombie
Headcrab Zombies are Zombies from Half-Life and Half-Life 2. In Half-Life, scienctist had been turned into Zombies from the Headcrabs. In Half-Life 2, Zombies are from Citizens, but these Zombies can also throw debris at you. Zombies are usally found in non-combine locations (like Ravenholm).
To kill a Headcrab Zombie, you need to use a .357 Magnum or Shotgun. If you don't have those use your Pistol or SMG. Crowbar is ok with Zombies but you might take some damage. Really you need to aim for the head (where the headcrab is), if you aim for the lower body the Headcrab might survive. Throw debris at Zombies if you want but be careful of the suriving Headcrabs and their Torsos. Headcrab Zombies also come in Torsos. Zombies sometimes have no legs so the torsos crawl around in crouch areas like the Auto-Gun junk yard in HL2: Episode Two.
Poison Headcrabs and Poison Zombies
Poison Headcrabs and Poison Zombies are from Half-Life 2. Poison Headcrabs are darker and cat-sized and spider like creatures. If a Poison Headcrab bites you, your health will drop all the way 1 percent! However, Poison Headcrabs alone can not kill you, other enemies around finish you off. Hide if a Poison Headcrab bites you, so your health returns to it's normal levels. Poison Zombies are hunch back Zomnies with Poison Headcrabs around it. Poison Zombies are very slow, but strong. They can throw Poison Headcrabs at you (only 2-3), Poison Zombies have large health, use your shotgun alot of times for fire your Assault Rifle at them. Really use a exposive barrel or gas can to beat a Poison Zombie.
Poison Headcrabs and Poison Zombies are more poisonous then normal ones. Poison Headcrabs can be used the same way as normal headcrabs, Poison Zombies are strong and do not come in Torsos.
Fast Headcrabs and Fast Zombies
Fast Headcrabs and Fast Zombies are found in Half-Life 2. Fast Headcrabs are what you see in the Ravenholm chapter and so on. Fast Headcrabs are quicker than normal ones but have same health and do same damage. Fast Zombies are Fast Headcrab's victum. Fast Zombies are quicker but have same health, but do less damage. Like regular Zombie, aim for the head. Plus Fast Zombies also come in torsos (starting in Episode Two).
Fast Headcrabs and Fast Zombies are quicker than normal ones. Fast Headcrabs have more spiny legs than normal Headcrabs, Fast Zombies look like skelatons.