The sound that starts playing when your raiders are about to run out of oxygen. It's a sound of heartbeat and someone desperately trying to catch his breath. In a game rated 8 and up. And chances are that the first time you hear it, it will be on the level where you spend the first half running away from hordes of monsters and rushing lava... only to realize, once you're safe, that you need to build the Supply Station PRONTO, using the limited amount of resources and safe ground you have. Sweet dreams.