"You don't have to say it out loud," Strange gently teases. But he should probably explain this in a better way. He pauses for a moment, frowning a little before he starts explaining.

"You just say it with your magic. Everything in this world has a magical aura or some inherent magic of it's own. You just reach out with yours to try and touch it and that's when you 'speak.'"

Maybe a demonstration would work? Strange closes his eyes for a moment, before making a hand gesture. "Help cool Billie down," he murmurs, audible enough for Billie to hear but still slightly under his breath. And then, barely a moment later, a small gust swirls around Billie, giving her a pleasant breeze.