Taken from the Left4dead forums

Unusual Dead Air Sighting

One day I joined a public expert coop on Dead Air. Things were coming along surprisingly well, considering I had not previously played with any of my teammates at all. After mowing through all the levels in a fashion that would bring a single proud tear into Chicago Ted’s eye, we entered the finale confident of reaching a quick resolution. Final tank down, our four survivors were awaiting the ramp opening when Bill, suddenly and without mercy, pumps his automatic shotgun into our group. Just as the last shotgun round echoed above our three corpses, Bill used his mic for the first time. In a voice I recognized immediately, Bill Murray revealed himself and spoke in almost a whisper–“No-one will ever believe you.” At this he promptly teabagged Francis in a sort of final insult and stepped aboard the airplane, flying off and collecting his achievement.