Knock knock.

Who’s there?

You know.

You know who?

That’s right, Avada Kedavra!

My sister first heard this from one of her friends. To someone unacquainted with J.K. Rowling’s world of Harry Potter, this joke is probably not funny at all. Thus, it is only told within groups of people who are familiar with the Harry Potter canon, specifically those people who have read the series through Goblet of Fire, because the term “Avada Kedavra” was not introduced until then (thus the joke exists terminus post quem 2000).

This joke follows the pattern typical of knock-knock jokes, but is customized for fans of the boy wizard. In the books, the villain, Lord Voldemort, is nearly always referred to as “He Who Must Not Be Named” or “You-know-who.” Here in the knock-knock joke, the latter is used since it fits the knock-knock formula. In the Harry Potter books, nearly all of the characters are so afraid of Voldemort that they are unwilling to even say his name (only a very small handful of characters are bold enough to say “Voldemort”). For someone who has never read the fourth Harry Potter book, the term “Avada Kedavra” makes no sense. However, a person familiar with the text knows that this is the incantation for one of the three Unforgivable Curses: the Killing Curse. This is Voldemort’s specialty, and he does not hesitate to use it: instantly killing the victim, he or she has no time to react and block the spell, and the spell leaves no mark—other than the fact that the individual is dead, he or she looks like a healthy, living person. Harry Potter is the only person to have survived this curse, and the idea of life versus death is a key thread linking together all of the books in the series.

The very nature of the joke as a knock-knock is also humorous. On the night Harry survived the Killing Curse, Voldemort came to his house and essentially walked in through the front door, then proceeding to kill James and Lily (Harry’s parents). The fact that the joke is a knock-knock, simulating Voldemort being at the door, makes this joke funnier. It appears that Voldemort, a fictitious character, has arrived at your doorstep, instead of the Potters’, and is preparing to kill you, not James and Lily Potter. True, this may be slightly disturbing, but for a “HP fan,” the knowledge of the context of the story makes the joke seem all the more humorous.