School bells have long been used to mark the start and end of lessons, so their sound is familiar to almost anyone who has attended school. As phones and soundboards made short clips easy to share, this familiar chime became a handy shorthand for school itself in short videos, memes and classroom comedy. It needs no context to be understood, which is why creators keep returning to it for back-to-school content, exam jokes and skits about teachers, lessons and the wait for the final bell.