The scream comes from the headcrab zombies in Valve's Half-Life series, enemies created when a headcrab takes control of a human host. Their pained, reversed-sounding cries became one of the most recognisable sounds in the games, especially in Half-Life 2's Ravenholm levels. Clips of the audio were later shared as loops on soundboards and in mods, where creators reuse the familiar wail to instantly signal a zombie threat without showing the creature itself.