10. How Owl Post Works
When it comes to creatures you're allowed to take to Hogwarts, it's really a no-contest: owls are not only cuter than cats and toads but infinitely more useful too, capable of carrying letters and parcels to seemingly anyone in the world.
But how exactly does owl post work?
We've seen throughout the series that the owls can not only deliver parcels to long distances without needing an address, but also that some of them at least can find people who are literally in hiding.
It's said they have an affinity for magic and need to be trained to carry letters (by who?), but that doesn't really clarify just how Sirius Black can remain in contact while he's the most wanted wizard alive.