Self-shadowed normal mapping. That got you sitting up in your seats didn't it? Forget zombie hordes for a second, put the intricate and sophisticated animation system to one side, and focus on what's going to make Left 4 Dead special: self-shadowed normal mapping.
"The flashlights are really tied into the gameplay," begins Valve's technical superbrain Jason Mitchell, paving the way for the incoming jargon.
"In our past games they were attached to the player, but in Left 4 Dead they're attached to the weapons.