If you still devote hours every week to obsessing over the minutiae of the Potterverse (not that we have ever done this *frantically hides to-scale replica of Hogwarts behind back*), then you know that some of the go-to spells in the wizarding world are absolute, logical necessities in one's daily magical existence.
And conversely, that some spells exist for mysterious reasons which still make absolutely no sense, and we demand an explanation. Below, we've rounded up 11 of the worst offenders: the "Harry Potter" charms, spells, and hexes that are still making us go hmmmmm after all this time.
1. Cistem Aperio
Performed in flashback by Tom Riddle in "Harry Potter and the Chamber of Secrets," this spell opens chests and boxes... but only chests and boxes. In a world where the far more general and useful alohomora exists, why do they even need this?
Speaking of redundant spells: You've got levicorpus and alarte ascendare and wingardium leviosa, so do you really need this one, too? (That is, unless you find wingardium leviosa too difficult to pronounce.)
3. Arania Exumai
This extremely niche-y spell functions to blast away giant (and, presumably, other-sized) spiders, but only spiders. Does this mean that you can't ward off bugs in general without casting distinct, species-specific spells for each? What if you're being attacked by spiders and fire ants? Or spiders and scorpions? Or spiders disguised as fire ants riding on the backs of scorpions?
4. Homenum Revelio
This spell was used by Hermione in "Deathly Hallows" to confirm that they were alone inside the house at Grimmauld Place. But since it apparently doesn't work to reveal the presence of non-human entities (see: Kreacher), and since the Potterverse is a place where werewolves and trolls are things that exist, putting your confidence in it to keep you safe seems like a bad move.
You didn't say "Trollium Revelio."
We're gonna need a little more information on the limits of this spell. Like, how serious of an injury is too serious for episkey? Can you mend a femur? A spine? A cranium? And why is this spell not being taught as part of first-year Wizarding 101 to every accident-prone kid who walks through the doors at Hogwarts?
Anteoculatia, which causes the castee's hair to spontaneously reshape itself into antlers, didn't make it into the movies -- but that doesn't mean we don't have questions about its existence in the wizarding world. Who invented it? And how? Because come on, there's definitely a story there.
So, like, would this also work if you wanted to attack your ex with a swarm of bees? Asking for a friend.
And this one: Is it only for boggarts? Or could we aim it at anyone intimidating who needs to be taken down a peg, like, say, the IRS?
There's no question about the usefulness of a spell that causes permanent, irretrievable wounds in the flesh of your enemies, which is why it's a little bit weird that it was apparently only invented by Snape after -- what? Multiple thousands of years of wizardly experimentation?
10. Piertotum Locomotor
"I've always wanted to use that spell!" says McGonagall, and dude, we totally understand why. But assuming it works on all statues, and not just the Hogwarts stone guard, you'd think she would've used it ages ago to animate her G.I. Joes or something.
11. The Slug Vomiting Charm
This is it, you guys: The number one most inexplicable spell in the Potterverse. We waited through six movies after "Chamber of Secrets" for someone to explain how, when, and why the wizarding world developed a charm that not only causes uncontrollable slug barfing, but has no fancy incantation to accompany it apart from "Eat slugs!" ALAS, THE MYSTERY REMAINS.