Ask Mr Brain...all will be explained

King Hussein died of non-Hodgkin's lymphoma. What is non-Hodgkin's lymphoma and is there a Hodgkin's lymphoma? Lymphomas are cancers of the lymphatic system. There's a Hodgkin's disease, named after Thomas Hodgkin of London, who first described it in 1832. And there are a number of other forms, grouped under the umbrella name of non-Hodgkin's lymphoma.

King Hussein's cancer was believed to be the most common type of the latter group, known as B cell non-Hodgkin's lymphoma.

While many people with lymphoma live for decades, others - such as King Hussein - develop highly aggressive forms and succumb quickly. He died less than eight months after the diagnosis was first made.

Why is New York City called the Big Apple? The Big Apple has been New York's nickname since the early 1960s, but its origin is unclear.

It is known, however, that Big Apple was used for a while in New Orleans around 1910 by jazz musicians as a loose translation of the Spanish 'manzana principal', which means the main 'apple orchard', referring to the main city block downtown where all the action is.

In addition, Morris Dictionary of Word and Phrase Origins says the Big Apple nickname for New York possibly relates to a popular dance of the 1930s called the Big Apple.

Why do birds sing? While poets throughout the ages have fondly imagined that birds sing so beautifully simply to express their joy of life and brighten up the world, reality is rather more mun dane. It is mainly male birds who sing, and they do so for one of two reasons.

A male bird sings to stake out its territory and warn other male birds that this is his patch, and woe betide any invaders.

The other use of song is to attract a mate.

Each species tends to have its own distinct song, so that keen ornithologists - those who study birds - can often identify a species simply by hearing its song.

So, rather unpoetically bird song tends to boil down to 'This is my territory, so clear off' and 'I'm available, girls'.

How come astronauts are able to eat food and digest it when there is no gravity in space to help the food go down? Fortunately for astronauts, our bodies do not rely on gravity to help food travel through our digestive systems.

The outer walls of the digestive system are made of layers of muscle which automatically contract in waves - called peristalsis - to push our food down through the system.

Here's an experiment you could try at home: stand on your head and try to eat something. It's possible, but messy.

Without peristalsis, we would have very hungry astronauts and there would be little chance of long missions to remote planets.