In my experience, people often run their mouths constantly -- "Oh god, what's that, what's over there, is that the alien?" And there's feedback from the audience, "Oh shit, watch out!"

Not to mention the occasional breath on someone's neck or tap on the shoulder.

When the experience is over, you pull the headset up -- an action not too far removed from looking away from a monitor -- and immediately start sharing. "Man, in that room with the shadows, I was watching the alien for a good 20 seconds before any of you saw it!"