Studies show that seeing their own mirror images gives creatures an increased ability to develop social responses—Parrots and fighting fish, sea lions and crayfish placed in tanks whose outer walls are wrapped in a reflective lining are observed to rear up more, curl their tails, walk clockwise or counter- clockwise because they see an image of something that resembles them going through those motions. It's the reason we suddenly have the urge to yawn after seeing someone scrunch their eyes while opening their mouth; why hearing the sound of retching from a nearby bathroom stall might incite the need to gag. With the onset of the pandemic, handshakes and high fives gave way to fist or elbow bumps. And before that, the inside of the elbow became preferred cushion for a sneeze. History is a long, cobbled street lined with grey buildings: at every window, a cat or a child or a man or woman has their faces pressed to the glass, waiting to see who will wave, who will raise or lower a basket filled with bread and water; who will put their thumbs and fingertips together in the shape of a heart; who will point an imaginary gun at the head, who will duck under the sill or throw up their hands.