Fog horns have long been used on ships and at lighthouses to warn other vessels in poor visibility, producing a low tone that travels far over water. That serious, real-world purpose made the sound easy to repurpose online, where the long bellow became shorthand for something big, ominous, or over-the-top. Short clips of the blast spread through meme edits and reaction videos, often placed over reveals or awkward entrances. Unlike a sharp air horn, its low tone sets a mood without needing any words.