Headcrabs first appeared in Valve's Half-Life in 1998 as small parasitic aliens that leap at Gordon Freeman and turn victims into zombies. Their distinctive screeches and chattering became one of the series' most recognisable audio cues, returning in Half-Life 2 and later entries. Fans have remixed and recreated the sound for mods, machinima and custom soundboards ever since. This custom version follows that tradition, keeping the short attack cry that players associate with a sudden ambush in dark corridors and vent shafts.