Around the age of ten I had the following thought: if two twins truly had the exact same DNA, would their every action be identical? I remember expressing this thought to others and being told that that’s ridiculous. Is it though? Now that I’m a little older, I can refine the scenario a bit. Suppose there are two identical parallel universes. From the moment the same child is born in both universes, is it possible for their actions to differ at all? My intuition is that they would not differ. And I believe this was the intuition behind my ten-year-old brain’s question. I suppose people could have different intuitions about this matter. Perhaps mine will change with time.