The silence after someone says 'I'm fine'

It’s not the word itself—'fine'—but the way it hangs in the air afterward, like a door left ajar. I’ve heard it so many times in the library, over the phone, in passing: 'I’m fine.' And then nothing. Just that quiet, where you’re supposed to believe it but can’t help wondering what’s being held back. Last week, a kid returned a book late—four weeks overdue—and said it with the same flat tone. I didn’t ask. I just handed him the receipt and smiled. He looked surprised. Maybe he thought I’d say something. But I didn’t. And that was the point.