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.

In 1894, Lord Kelvin predicted that radio had no future; he also predicted that heavier-than-air flying machines were impossible.

The paperclip was invented by Norwegian Johann Vaaler.

Traffic lights were used before the advent of the motorcar.

One hour before Alexander Graham Bell registered his patent for the telephone in 1876, Elisha Gray patented his design. After years of litigation, the patent went to Bell.

Count Alessandro Volta invented the first battery in the 18th century.

Ulysses Simpson Grant thought Venice would be a nice city if it were drained.

The only time in American history that the president and vice president were members of different political parties occurred in 1797, when Thomas Jefferson, Republican, became vice president under John Adams, a Federalist.

The first and only vice president to be drunk at his inauguration was Andrew Johnson. His doctor had prescribed an alcoholic drink to relieve pain.

Lyndon Baines Johnson was so obsessed with secrecy that he often wrote “burn this” on personal letters. This was so personal that no one on Earth including me knew about this.

The first wife of a president to have a college degree Lucy Webb Hayes, wife of Rutherford Hayes. She had a degree in geology, which was rare for a woman to have degrees at that time.

Music was sent down a telephone line for the first time in 1876, the year the phone was invented.

Accounts from Holland and Spain suggest that during the 1500s and 1600s urine was commonly used as a tooth-cleaning agent.

In 1958 the US sent two mice called Laska and Benjy into space.

In 1961 the US launched a male chimpanzee called Ham into space.

Great Britain was the first county to issue postage stamps, on 1 May 1840. Hence, UK stamps are the only stamps in the world not to bear the name of the country of origin.

The first parachute jump from an airplane was made by Captain Berry at St. Louis, Missouri, in 1912.

Coffee is the seed of a cherry from the tree genus Coffee

The number of people who starved to death in the last 25 years of the 20th century is less than the number who starved to death in the last 25 years of the 19th century.

The first European to encounter tea was the Portuguese Jesuit Jasper de Cruz in 1560.

Pepsi-Cola was invented by Caleb Bradham in 1890 as “Brad’s Drink” as a digestive aid and energy booster. In was renamed as Pepsi-Cola in 1898.

Watermelons are 97% water, lettuce 97%, tomatoes 95%, carrots 90%, and bread 30%.