There is a fantastic moment in Half-Life 2, during the 'Water Hazard' section of Valve's FPS game, when you first arrive at one of the resistance outposts, Station 12. Previously, you - or, if you prefer, Gordon Freeman - have been told that communications with Station 12 have mysteriously ceased. Overlooking City 17's irradiated river, the Station is supported on stilts. Immediately, you know that something is wrong. The river is silent. No-one exits the Station to greet you. A large wooden container dangles ominously from a pulley - the grand piano over Buster Keaton's head; some stark realisation just waiting to drop.