Science

They are: Basal tears (protecting and nourishing cornea) Reflex tears (glands' reaction to irritating compounds, like smoke) Emotional tears (produced in response to various emotional states)

Many species require small amounts of them to survive. They can be saprophytes feeding on dead organic matter, or parasites developing at the expense of other living organisms.

It interacts with visible matter only gravitationally and remains invisible and undetectable in any other way. It is estimated that 90 percent of the mass of the Milky Way is dark matter.

It is enough for the first and last letters of a word to be in the correct place.

It was named after Asaph Hall’s wife, Chloe Angeline Stickney Hall, a mathematician. A collision that formed Stickney crater could have shattered the moon.

It was used both during religious ceremonies and in hospitals because it was believed to accelerate recovery and help to concentrate.