Full quote: "Suppose it is a calm day, absolutely still, not a twig or leaf stirring. To me it will seem quiet as a tomb though hedgerows are full of noisy but invisible birds. Then comes a breath of air, enough to unsettle a leaf; I will see and hear that movement like an exclamation. The illusory soundlessness has been interrupted. I see, as if I heard, a visionary noise of wind in a disturbance of foliage . . . I have sometimes to make a deliberate effort to remember I am not 'hearing' anything, because there is nothing to hear."