Everything that seems strange about quantum mechanics comes down to measurement. If we take a look, the quantum system behaves one way. If we don’t, the system does something else. What’s more, different ways of looking can elicit apparently mutually contradictory answers. If we look at a system one way, we see this; but if we look at the same system another way, we see not merely that but not this. The object went through one slit; no, it went through both. How can that be? How can ‘the way nature behaves’ depend on how – or if – we choose to observe it?