Your brain can sort colours, sounds and memories, and in principle you could explain all that sorting without anyone needing to be home. Yet tasting your morning coffee feels like something from the inside. Science has several serious rival accounts of why. They disagree about almost everything, except that the question is worth asking.

In Renaissance painting contracts, one colour got written up like a precious material: ultramarine, made from a stone mined in what is now Afghanistan. The odd part is that crushing the stone doesn't give you that blue. Getting it out took a strange kneading ritual in wax, resin and lye.

On the world map most of us grew up with, Greenland looks about as big as Africa. In reality Africa is fourteen times larger. The map isn't careless. It was built to keep sailors' compass bearings straight, and the price of that promise is that the world swells the closer you get to the poles.

Medieval English speakers tied on "a napron". Say that out loud a few times and you'll hear the problem: it sounds almost exactly like "an apron". Over the generations the n slid across the gap between the words, and the same slip, running the other way, turned "an ekename" into "a nickname".

Run your own fingers along your ribs and almost nothing happens. Let someone else do exactly the same thing and you squirm. The difference isn't in your skin. It's in a quiet forecast your brain makes every time you move.