In issue 29 of *Plus*, we heard how a simple mathematical equation became the subject of a debate in the UK parliament. **Chris Budd** and **Chris Sangwin** continue the story of the mighty quadratic equation.

How does the uniform ball of cells that make up an embryo differentiate to create the dramatic patterns of a zebra or leopard? How come there are spotty animals with stripy tails, but no stripy animals with spotty tails? **Lewis Dartnell** solves these, and other, puzzles of animal patterning.

There are many different types of lottery around the world, but they all share a common aim: to make money. **John Haigh** explains why lotteries are the way they are.

It has often been observed that mathematics is astonishingly effective as a tool for understanding the universe. But, asks **Phil Wilson**, why should this be? Is mathematics a universal truth, and how would we tell?

**André Léger** studies the fluid mechanics of food travelling through the intestines for consumer goods giant Unilever.