At the end of "follow freeman" when dog lifts up this bit of the citadel so you can enter it through a hole underneath, barney says it just as dog is dropping it back down hence the *crash*.
that vortigaunt has a hell of alot to say and half of it is meaningless, he says something different each time you talk to him and it took about five mins for me to get back to the first thing he said.
yes there is no multiplayer for hl2 as of yet, i think you are the crazy one, half of what you are saying dusnt make sense.
that quote is gona b my sig lol