Knowledge connects us all.

When chlorophyll breaks down, the yellow and orange pigments already in the leaf become visible.

Sulphur compounds released when the cells are broken are what carry the smell.

Freezing locks water molecules into an open crystal, so ice is less dense than the water it floats on.

Dreams occur mainly in REM sleep and appear tied to consolidating memory and processing emotion.

Rivers wash dissolved salts off rock into the sea, and evaporation removes the water while the salt stays.

A sudden spasm of the diaphragm slams the vocal cords shut, and that snap is the hiccup sound.

The pigment cells in each follicle stop making melanin, and hair grows in without colour.

Cutting releases a volatile compound that reacts with the moisture in your eyes to form a mild acid.

Tiny muscles at the base of each hair contract and stand it up — a leftover from ancestors with far more fur.

Yawning appears to cool and rouse the brain, and catching one from someone else reflects social empathy.

The iron-bearing haem group in haemoglobin is what makes blood red.

Air molecules scatter blue light far more than red, so the whole sky glows blue.