Metro Cops are the Combine Civil Protection officers who patrol City 17 in Half-Life 2, Valve's 2004 first-person shooter, and their death audio comes directly from that game's combat encounters. As players fought back against the Combine occupation, short clips of enemy voices, radio chatter and death sounds began circulating among fans and on soundboards, where they were reused far beyond the original levels. The clip endures because it is instantly recognisable to Half-Life players and works as a compact, grim shorthand for an enemy going down.