Yesterday morning, I was sitting alone in the library of the building I live in. It's a beautiful room, simple and spacious. I was sitting on the floor, on a cushion, not doing anything, content to sit and look about the room, feel the breeze, and listen to the sounds coming through the open windows.

And for some reason, I started thinking about knife grinders. In every city I lived in while growing up in North American and in Europe, there has been a knife grinder. They always seem to have a bell and it makes a very distinctive sound. No mistaking it. Until a year or so ago, I'd never actually seen one, never bothered going to a window to look. But I can remember saying, so many times, "What is that sound?", and being told "That's the knife-grinder's bell". I would think, "How nice – someone who goes around neighbourhoods sharpening knives and scissors". I suppose it evoked the same kind of feeling I had about the rag and bone men I'd read about in books."

As I was remembering this, I heard the very faint ringing of a bell. At first I thought, "Oh, I'm just hearing that because I've been thinking about knife-grinders and bells." But no, the ringing of the bell grew louder and I knew that it was the knife-grinder. That really made me wonder about the acuity of my hearing because, obviously, I had heard the sound before it registered as a bell.

Then I started to laugh at myself. I'd got myself into a comfortable state of nostalgia and melancholy over the ringing of a knife-grinder's bell. And then remembered that when I'd actually seen one, it wasn't the little wooden cart being pushed by a man on foot with tools swinging and swaying from a rack, that I had imagined as a child. It was a truck with a loudspeaker mounted on the roof. I'd been so disappointed.

So I let go of my childhood memories of something I had never seen and just sat in the room with the heron-blue floor and cases of wonderful books. I looked at the mottled light and shadow dancing on the walls, crazy branches of curly willow in a blue glass vase reflecting the light. And listened to the sounds of traffic and the knife grinder's bell.