First you will learn about smiles, how much you smile, what's contained in a smile, what's implied in the different degrees of smile: in a curl of the lip at a funny thought, in the mouth's outstretched corners to greet the close acquaintance, in the sardonic phrase, the empathic moment. All these things you will learn when they cannot be seen.
And eyes. You will learn about eyes. How readily you can recognise eyes across a courtyard or carpark, how much you can guess of a heart or a day from the eyes poking out above the nose.
And breath. You will learn about breath. You will taste it, smell it, absorb it all day. You will choose your words and your silence to preserve moments when you can simply breathe. You will long to stand in the garden beside your office and do nothing in that afternoon air but take off your mask and breathe.
And faces - you will catch, in their absence, the beauty, the wonder of faces, the heart-catching, God-splendoured glory of faces. You will long for the faces that you loved and despised, will search the room for these faces, will wish that these faces could transfigure their otherness straight into yours. You will cover your face and stifle your breath and halve your smile in hope of the day, to work for the day, when all of our faces are back.