ALL ARTICLES.

Swap a ship's planks one at a time and every repair looks harmless. Then someone builds a second ship from the old planks, and "the same ship" stops being an easy phrase.

One grain of sand is not a heap, and one more grain never seems to make the difference. Follow that thought all the way and you end up somewhere absurd.

Things can get better and people can still feel worse off. It depends on who they're comparing themselves with.

Two spoons sit in the same drawer for a week and end up at exactly the same temperature, yet the metal one feels colder in your hand. Your skin isn't measuring the spoon. It's reporting the temperature of the handshake between you.

A coffee spill doesn't dry to an even brown blot. It dries to a dark rim around a pale middle, because the drop's edge gets stuck and a hidden current spends the whole drying time carrying the coffee outwards.

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.

Flick water onto a warm pan and it hisses away in seconds. Flick it onto a much hotter one and it beads up and skates around for far longer. Past a certain point, more heat makes the drop last longer, because it's riding on a cushion of its own vapour.

A comet's tail isn't exhaust trailing behind it. It points away from the Sun, wherever the comet happens to be going. And look closely, and there are two of them, because the Sun is pushing on the comet in two quite different ways.

In Jane Austen's Emma, a young man nearly confesses something, and the narrator tells us he "was more in love with her than Emma had supposed". It reads like a fact. It isn't. It's Emma's own guess, slipped into the narrator's voice without a single quotation mark, and once you can spot the trick, you'll find it all over the novels you read.

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".