When I was in sixth grade, a girl I knew accosted me one day in the stairwell, staring up at something on my face. When I tried to sidestep, she followed. I asked what she was looking at.

"Don't you know?" she said. I shook my head. "It's your nose!"

I stared at her uncomprehendingly. "Your nose! It's flat right here!" She rubbed her own nose bridge with her fingers. "See how mine has a bump? Yours doesn't."

I felt the same place on my own nose. She was right: Where she had a ridge, sprinkled with freckles, I had none. I never would have noticed the difference [...]