In 'The Violinist's Thumb,' I talk about the poignancy of cells leaking across the placenta into both the mother and the child.

If stem cells divide equally, so both daughter cells look more or less the same, each one becomes another stem cell. If the split is unequal, neurons form prematurely.

As a child in the early 1980s, I tended to talk with things in my mouth - food, dentist's tubes, balloons that would fly away, whatever - and if no one else was around, I'd talk anyway.

Most people, even most doctors, learn that the placenta is a nice, tight seal that prevents anything in the mother's body from invading the fetus, and vice-versa. That's mostly true. But the placenta doesn't seal off the baby perfectly, and every so often, something slips across.

Lithium makes a fine battery because it's a scarily reactive metal. Pure lithium ignites on contact if it touches water - a flake of it would sizzle and fry on the water-rich cells of your skin.

It's often meaningless to talk about a genetic trait without also discussing the environment in which that trait appears. Sometimes, genes don't work at all until the environment awakens them.