Poison headcrabs are a darker, venomous variant of the headcrabs from Valve's Half-Life series, most associated with Half-Life 2. Their bite is one of the game's instantly recognisable creature sounds, lifted from gameplay into soundboards, reaction videos and horror edits by players who grew up with the series. Because the clip is only about a second long, it works as a quick punchline or scare beat without needing any context, which has kept it circulating long after the game's release.