Most of us have heard of "stealth" - a technology used by the military to disguise craft from enemy radar. But nature's stealth fighters are not so well known - creatures that use motion camouflaging to approach their prey undetected. Lewis Dartnell looks at the vector mathematics behind the phenomenon.

Did you know that you can't average averages? Or that Paris is rainier than London? Explore the dangers that face the unwary when using a single number to summarise complex data.

Frances Elwell looks at the eddies and currents, from the pungent problem of sewage outflow to the search for bodies of people who have fallen into rivers, explaining that fluid mechanics lies behind it all.