One nifty feature we hadn't seen in previous demos of DOOM 3 was the simple and elegant way players can interact with the environment. I originally found myself looking for a "use" key to operate elevators, and got fragged for my trouble more than once. id programmer Robert Duffy pointed out that there isn't a "use" key -- the game realizes when you're near an item to interact with, lowers your gun automatically, and allows you to interact using the primary fire button. After years of using special keys to interact with objects in FPS games, it felt refreshing to walk up to a light switch and watch my player instinctively lower his gun sight to allow me to flip the power on.