Maybe houseflies evolved to have 6 legs, but originally had 4?

In Ancient Greece, courtesans wore sandals with nails studded into the sole so that their footprints would leave the message "Follow me".

More than 100 years ago, the felt-hat-makers of England used Mercury to stabilise wool, with many eventually being poisoned by the fumes - as demonstrated by the Mad Hatter in Lewis Carroll's Alice in Wonderland.

The population of the world in 5000BC was 5 million.

In World War II, it cost the Allies $225,00 to kill one enemy soldier.

Cambridge University was established in 1209.