In Doom, a player or monster killed by a weapon or by blast damage acquires momentum. Since altitude doesn't affect planar momentum, this can result in certain kinds of counterintuitive motion. These include ascending staircases, sliding along high ledges at a uniform speed until they fall off, making the "oof" sound after falling off a ledge, and activating walkover linedef types (such as teleporters, crushers, and "trapdoor" exits).