If, like a package of food, you had a list of ingredients stamped in an out-of-the-way spot like the bottom of your foot—with the elements that make up most of your weight coming first—it would read ...

Nestled directly below oxygen and sulfur on the periodic table, selenium doesn't attract too much attention. But this relatively rare element is an important nutrient for animals, including humans.

In the final programme in our Elements series, Justin Rowlatt looks at the rarest and oddest members of the periodic table. Selenium, bismuth, molybdenum, antimony, rhenium, hafnium, zirconium, ...