The melody comes from the theme to The X-Files, the American science-fiction series about FBI agents investigating unexplained cases, which first aired in 1993 with music by Mark Snow. Its sparse whistle became shorthand for government secrets and the paranormal long before short-form video existed. As creators began reusing TV themes as reaction sounds, the cue spread across edits about conspiracies, coincidences and strange news, because listeners recognise it instantly even without seeing the show. That instant association keeps it useful for mystery and comedy alike.