First time I came across a Witch in Left 4 Dead. I believe it was on "Dead Air", one of the earlier parts where you have to move a crane on some roof tops I think. As me and my buddy were slowly poking around, checking out the area, I heard a faint cry. Mind you, I've never known what the Witch was beforehand, and my buddy didn't bother telling me, so I kept looking around. I turn a corner and look one way, and behind my back I hear growling. I snapped a 180 turn, and there she was, hiding behind a chimney(?) and pissed as Hell because my flashlight was in her face. I yelled "OH FUCK ME!!" and blasted away with the auto shotty at her, and without any resistance, she gently went down. After shooting off all of my shells, an achievement popped up, "Cr0wned", and I was still in full adrenaline mode.
TL;DR Witches be scary, yo.