Why would they? They could just wait outside or chuck a grenade in them 
I do believe that barnacle is relieving himself.
Bah, I knew I should have went with the dark/pale yellow.
Gordon: What the fuck is dripping on my head? looks up
:fffuuu:
Fixed it. Now it’s Barnacle Tongue colored.
Now the Barnacle is pissing. That’s even worse.
Thanks for the courtesy Raminator. 
Hahaha ^this indeed. That’s hilarious. Maybe there could be unicorns in the vents; wait, no, this isn’t Diablo 3, I’m sorry.
On a more serious note, I don’t think houndeyes would work, unless it was a vent accessible from ground level, but it would be neat (to a point) if you tried running into a vent away from a houndeye and it just followed you in. Legless zombies, that works, especially because headcrabs in vents are more a source of “oh shit!” than damage; a zombie could very well knock you around in a cramped vent.
Oooh, what if you passed a vertical pipe and had a severed zombie drop into the vent after you passed it? Like the headcrabs that fall onto the ventilation fan in Office Complex (I think). You pass the opening, hear a thud behind you accompanied by zombie moans and go “OMGWTFOHSHIT ZOMBIE WITH NO LEGS!!”
I liked that red vent in Interloper, it gave me a calm peaceful secure feeling for some reason.
I think it was the floating red dots. I agree, I always liked hanging out in that vent - it was a quiet connector between the Grunt factory and the Controller hellhole room leading to Nihilanth lol.
let’s all hang out in the red-dots vent.
It’s what I did :] I didn’t finish the game until 4 days after I found that vent.
a headcrab is a symbiote a host body who can access brain`s commands of his host to control him more exactly it becomes an extension of the brain or secondary brain other aliens cannot becomes host bodies but they can eat them 
And what does that have to do with anything anyone was talking about, fly?
Well, we were talking about barnacles in vents, right?
You can all wave goodbye to your sense of security on Xen, because I’d put money on those vents being sphincters in BM.
Um, what?
halo 3 sphincter doors :sick:
Hot Carl, anyone? :awesome:
Oh yes, the anuses.