Boomer!!!!!

I played some Left 4 Dead with my buddy Rob this weekend. He already reviewed it so I'm not going there but someone explain to me how this monstrosity keeps sneaking up on me.

Really he makes loud disgusting noises, one can hear for at least 5 minutes before he appears out of no where so you know he's coming, and he's at least 400 pounds so should be easy to spot. Yet the stupid zombie boss known as a Boomer consistently barfs or explodes all over my toon, usually Francis, blinding me and making me the primary target for the zombie horde. I hate you Boomer!