I was flossing, and watching myself in the mirror. There was a little black speck in between my two front teeth, like a miniature grape-pip or the shrapnel from a peppercorn. I flossed it, but couldn't dislodge it. I moved the floss up and down, and pulled the strand left and right. Then I realised it wasn't a speck: it was the shape of that part of the gap between my teeth. I had been flossing vacancy and expecting it to come, solidly, out into the sink.