Fast heartbeat effects have been a staple of horror and thriller editing for decades, borrowed from medical dramas and suspense films where a racing pulse stands in for fear the audience can feel. On short-form video and in games, creators use the sound on its own or paired with a dun dun dunnnnnnnn sting to mark a reveal, a near miss or a moment of panic. Because the rhythm is universally understood, it needs no explanation and works across memes, animations and live-action edits alike.