Tripods are the towering three-legged war machines from H. G. Wells's The War of the Worlds, first published in 1898, and they have since become shorthand for alien invasion in film, television, games and online video. Their unstoppable advance and piercing horn make them instantly recognisable, even to people who have never read the novel. On social media, the phrase tripods are here works as a dramatic punchline for any overwhelming arrival, from a boss entering a room to friends descending on a party, keeping the sound both nostalgic and current.