Nothing.
If you have met me in real life, you may have noticed I’m not the loudest person (immediate family members beg to disagree, mainly siblings). I’ve been told, by more people, that I’m “painfully quiet.” I can go hours with someone and not say anything–it drives people crazy. I’ve found myself apologizing for my silence. It seems like I’m not listening, and I can see how that might appear on the outside. But, I am listening, and fully engaged in the “conversation.”
I don’t intend to be a “brick wall” when you talk to me. My silence is not a sign that I’m uninterested in what you say. I’m simply absorbing your words and actions–watching how you gaze to your side when you are uncomfortable or struggle to express a thought (minus poker players–they are pretty crafty and masking what they are thinking or planning).
I think a factor in my is my own inability to precisely say what I’m trying to say. Ask me what I’m thinking, and I might not be able to express it orally; but hand me a pen and paper, and I’ll write you a novel.