The line comes from Harry Potter and the Prisoner of Azkaban, released in 2004, where Severus Snape covers a Defence Against the Dark Arts lesson and orders students to study werewolves. Fans clipped the page instruction and shared it across forums, video edits and soundboards, often in Spanish as Pagina 394. Its specificity made it a running joke about ominous school assignments, and the number alone became shorthand for Snape's lesson. It remains popular because the delivery is instantly recognisable even without the film scene around it.