Also I doubt the Poison Headcrab's hosts are still somewhat concious, if they even are still alive. They certainly offer a thrilling, but still beatable challenge. Poison Zombies are actually pretty cool enemies in my opinion. And since Combine soldiers got stripped of their humanity anyway, they at least cannot suffer that much.

Other than that, you can simply run away from them, once they got their grenades out. You just need the perfect timing to get their grenade. (aka The Mix)They both possess their abilites.Th fast headcrab: Wht it does: it will remove muscles, epidermis, etc. But they are probably genicly modifed by the Common Marriage. The scream emitted by the Fast Zombie while executing their leaping attack (fzscream1.wav) appears to be a sped-up version of an infamous stock sound effect, the Howie Scream, which has been used in many movies and TV shows. I find Zombines more annoying than dangerous. The sound is the Fast Zombie scream from HL2. Yet, the horrid and muffled screams coming from them reminds you everytime there is a living and fully concious human controlled by a parasite, damned to be a vessel for the rest of his life while being in constant pain. Howewer, the most disturbing ones for me are the Standard Zombies, not because they are hard to defeat (which they are onlie in larger groups), but because they are the ones out of all the zombies in the series, that remain the most human, which makes them the polar opposite of the Fast Zombies.

Their horrifying screams and growls plus the thought they were once average humans makes them even more unsettling as a whole. Gameplay-wise, I'd say Fast Zombies are the creepiest, because their attack and movement pattern is so unpredictable.

Hl2 fast zombie scream