The colored part of the eye is called the iris. Behind the iris is the soft, rubbery lens which focuses the light on to a layer, called the retina, in the back of the eye. The retina contains about 125 million rods and 7 million cones. The rods pick up shades of grey and help us see in dim light. The cones work best in bright light to pick up colours.

Your mouth produces 1 liter (1.8 pints) of saliva a day.

Over the last 150 years the average height of people in industrialized nations increased by 10 cm (4 in).

In the Middle Ages the length from the tip of the middle finger to the elbow was called an ell.

Fingernails grow nearly 4 times faster than toenails.