15 Things In Harry Potter That Don't Make Sense

5. The Boggart Conundrum

One of the first things we see the students learn from their new Defence Against the Dark Arts teacher in Prisoner of Azkaban is the spell, Riddikulus. This is the specific spell to use when defending against a Boggart. The creature's image is changed to something ridiculous, and is consequently defeated by the laughter created.

This all makes perfect sense at first. It isn't until Remus gives Harry some one-to-one tutoring on defending himself against Dementors that the problem arises. Instead of bringing an actual Dementor into the classroom to teach Harry how to use the Patronus charm, Lupin uses a Boggart that takes the form of a Dementor.

However, this doesn't... actually add up. A Boggart is defeated only by the use of Riddikulus. Just because the creature looks like a Dementor doesn't mean that it actually is one, so the Patronus charm would have zero effect. It is, quite simply, the wrong spell to use.

Surely this is something that Lupin would have known, as the best Defence teacher Harry ever had, yet against all logic and the rules presented to us by the movie itself, the charm works. Unfortunately, this just makes no sense.