Avada Kedavra is the Killing Curse from the Harry Potter series, one of the three Unforgivable Curses, first introduced in the books and made iconic by the films with its flash of green light and the whispered incantation. In the story it causes instant death, which gives the sound its grim reputation. Online, the clip spread through Harry Potter edits, gaming montages and reaction videos, where creators reuse the familiar blast to signal a sudden defeat or a decisive move. Its instant recognition keeps it useful long after the films.