The earliest tools we used to clean our teeth were fibrous twigs and lightly abrasive powders. Before the days of refined sugar, it was generally enough to just rub your teeth with your finger after a meal.

Today, for the most part, we use a toothbrush and toothpaste. This is a technique we originally reserved for polishing brass, marble, and granite.

At some point in history, somebody came to terms with the fact that their mouth was full of stones. This was a landmark concession. It shattered the old doctrine that the most beatiful and contemplative parts of a stone are its splashes of tangerine lichens, flicked across larger splashes of ash-coloured lichens.