Harry Potter and the Parentheses

I recently finished the Harry Potter series. I know, I know, I’m sort of late, but still, at least I’ve read it (*cough cough Spinette hasn’t yet cough).

While I could tell you what I thought about the book in proper review manner, I’d rather talk about this one issue I had with the book following the colon:

In one of the books, the sixth or fifth or some other number entirely between one and seven, Dumbledore is speaking and in the middle of the dialogue, there’s a pair of parentheses. Like this:

“How’d my brownie (made of vanilla and coffee) get all the way up on that flagpole?” Spinette exclaims.

How does one go about conveying parentheses in vocal conversations? Will someone please explain this to me?