I was buying greengrocery at the greengrocer’s over the road when the greengrocer said to me, “Two things always surprise me. The first is that a great deal of what a greengrocer sells isn’t green. Take oranges: they’re orange. Or purple grapes, I have some nice ones of those. The second thing is how much greengrocery is actually green. Why are so many things green?” I explained to him photosynthesis and how, quite deep down, it rested in quantum mechanics. “Strange, though,” he said, looking round his shop as if reassessing it. From my second floor office across the street I had a good view into the greengrocer’s window. The shop was empty and behind the banks of green objects I saw him kicking angrily at a wooden box.