HEADCANONS

http://magnaluna.deviantart.com/art/Young-Luna-portrait-655477359

Due to stumbling upon this image after deleting most of the pony blogs I follow, I came upon an idea... In this image, Luna's horn didn't have the usual unicorn swirl like many have seen but some sort of design. I actually like this artist's ideas and thought maybe this is how unicorns actually do preform magic through carved or earned runes that form upon their horns with either each casting or something else. This is why they don't speak during spells or call out incantations as the runes are already (In a very tiny way) imbued upon the horn possibly in the spiral lines going down the horn.

And the headcanon that unicorn hairs are hollow upon the casting magic, they don't burn upon the casted spell due to the fact they sort of 'bounce back' the magic towards the target.