Bombay: 18 million people live in the Indian megalopolis, and the trend towards urbanization is increasing. In the world, one in two people lives in an urban agglomeration. Between extreme backwardness and advanced technologies, Bombay produces a fifth of the total wealth provided by India in a year. Lorenzo Pinna tells us about the contradictions of this mega city. The third episode of the BBC series "Mammals" introduces us to the world of rodents, animals that have developed the ability to attack the hardest substances in order to survive.