"Some pig" Charlotte's Web, E.B. White
When I was about 10, my parents decided to hire someone to change the wallpaper in my room. One day when I came home from school, I discovered that most of the paper was stripped but the person doing the work drew my attention to one remaining shred of wallpaper still on the wall. In a dark corner behind the door, there was a small square of wallpaper upon which there was a tiny message. "This is my favourite room ever." It was signed by the little girl who had had the room before me. This hitherto invisible message briefly had light shone on it to be read. In return, I left a similar message for whoever came after me.