The sound comes from Half-Life 2, Valve's 2004 first-person shooter, which became famous for its physics system and the way defeated enemies and objects tumbled realistically through its environments. Players began recording and sharing those ragdoll moments in gameplay videos, and the distinctive flop was later clipped for reuse in edits, reaction videos and memes. It remains popular because it needs no explanation: like a punch sound or a bone crack, the impact is instantly understood, and its slightly ridiculous lifelessness makes serious-looking game footage feel playful.