An ordinary mirror is silvered at the back but the window of the night train has darkness behind the glass. My face and the faces of other travellers were now mirrored on this darkness in a succession of stillnesses. Consider this, said the darkness: any motion at any speed is a succession of stillnesses; any section through an action will show just such a plane of stillness as this dark window in which your seeking face is mirrored. And in each plane of stillness is the moment of clarity that makes you responsible for what you do.
Russell Hoban, The Medusa Frequency