Boos are among the most recognisable ghost enemies in the Mario games, known for drifting toward players when they look away and freezing when watched. Larger versions, often called Big Boos, appear in haunted houses and mansion levels, where their echoing calls help set the spooky mood. Short clips of their sounds have circulated for years among game fans, streamers and meme editors, who reuse them as a quick shorthand for anything ghostly, sneaky or haunted. That simple, playful scariness keeps the sound useful long after players first hear it in game.