MY SISTER LEARNED to whistle at age 2. She was precocious in other ways, as well. She knew how to read by the time she started kindergarten. She demonstrated a physical dexterity I never did. She was much more talented at the piano. But it was the whistling that really got to me. I was 6 when she started to whistle, and I remember it clearly. She sat in her highchair at my grandparents’ house…