Magic is a kind of energy. It is given shape by human thoughts and emotions, by imagination. Thoughts define that shape—and words help to define those thoughts. That’s why wizards usually use words to help them with their spells. Words provide a sort of insulation as the energy of magic burns through a spell caster’s mind.
I really do try to watch everything I say. Because one little tiny slip, and it's like the world is coming to an end!