If two molecules are practically identical, why does nature end up favoring one? To understand this phenomenon, which is known as homochirality, we can perform an exercise of imagination with a pair of shoes: the right and the left are mirror images of each other – as if one were the reflection of the other in a mirror – but they cannot be swapped because each fits a different foot. With some molecules, like amino acids, the same thing happens: they exist in two almost identical forms, but they cannot be superimposed. They are the so-called chiral molecules.