A non-fiction book, ideal for intermediate learners of English looking to improve and practise their English. The book is filled with useful vocabulary that is carefully graded and easy to understand, it also comes with audio, so that you can listen at the same time as reading.You're fast asleep, and nothing is happening. Or is it? In fact, your body is hard at work. Your lungs are taking oxygen from the air, and your heart is pumping blood round your body. Millions of pieces of information are travelling backwards and forwards to your brain all the time. Muscles are repairing themselves, and in your lymph nodes special cells are cleaning germs and waste from the body. You may think that nothing is happening, but in the extraordinary machine that is the human body, it is very busy indeed ...