Spoiler alert? Only if you planned to play community made campaign "Suicide Blitz 2" in Left 4 Dead 2, currently the officially featured fan-created add-on for Valve's zombie horror first-person shooter, the game that has a very neat Portal 2 Easter Egg buried within.
Watch as two Left 4 Dead 2-loving ladies discover the existence of a portal into the world of Aperture Science, commenting excitedly along the way about every machete, Companion Cube, propulsion gel and special infected zombie they run into. Really, you may want to turn the volume down just a notch.
You can grab the "Suicide Blitz 2" campaign right here, straight from Valve.