You know how easily it is to break a fingernail? I grabbed something wrong and cracked a piece off my right thumbnail. (I used to think that nails got brittle when you didn't eat enough calcium or protein, but we had been on vacation, eating an avalanche of Ca and Me, so forget that.) I filed the nail smooth, and it's not bothersome now. But the white part of the nail's profile dips low in the middle. And that's very important now.
My music player has a peculiar set of controls. When I first bought it, I thought I would hate it, but with use I discovered that the controls were brilliantly designed. There's a tiny touchpad on the device, and the plastic ring around the pad is actually four pushbuttons. You press the right edge, for example, to fast-forward. With your thumbnail. If you happen to have an ordinary sort of thumbnail, that is.