My grandmother used to say that the baobab outside our village near Caxito kept count of everyone who sat in its shade. Not their names, she said, because trees do not care for names. It counted their sorrows.

When I was nine I tried to prove her wrong. I sat beneath it every afternoon for a month and told it nothing at all. I did my homework there. I ate mangoes there and threw the stones at the goats.

On the last day of the month my father lost his job at the port. I did not tell the tree. I did not tell anyone. I just sat there longer than usual, until the light turned orange and the goats went home without me.

The next morning there was a new crack in the bark, low down, about the height of a nine-year-old boy sitting with his knees pulled up.

I am thirty-four now. I live in Cape Town and I teach physics, and I do not believe that trees can count. But when I go home, the first thing I do is find my crack in the baobab and put my hand on it, the way you would greet an old friend who knew you before you knew how to hide things.