‘The clouds are grey, the sun obscured and you are walking through the countryside in the overcast of winter. Passing from field to woodland, the trees shed coats of frosty bark to celebrate the passing of another icy season. It feels too early for spring, but echoes of swallows in the canopies sing songs of new beginnings. You pause to catch a glimpse of your woodland companions. With effortless precision, your eyes track the birds as they zip between empty branches and, combining countless neurons, you forecast the birds’ trajectory each time they fall out of view.

You walk on, emerging from the trees, and return to the open fields. You look back, appreciate the woods and see a river flowing into the trees from the east. Where does the river begin? Escaping the clouds, the sun will soon be free of the sky altogether; if you want to discover the river’s source, you had better get walking.’