This is starting to get spammy, and is slightly smaller than my previous theories, but nonetheless works! Looking at what has been gathered so far, we have the following:
Emotions <-→ organ <-→ 'organelles' in eye cells <-→ magic (plasma? Gas? Probably gas) + light → horn (excites nearby chemicals in the air, giving the glow we see) → spirals in horn → spell
not provided yet