This month, we're focusing on a chemical process which is all around us: how crystals form. Humans have been using crystallisation to harvest salt from seawater for millennia. In the modern industrial world, it's used to make sugar, gemstones and silicon chips. So it’s a bit of a surprise to find a completely undiscovered phenomenon, of a crystal healing itself, happening in crystals of paracetamol. How have we missed this? Why is it happening? And how could it be useful?