Marina Santee and Roger Basick talk about goldfish that live in the wild and their effect on the environment.
What is your favourite animal? In recognition of the UN's "World Wildlife Day", Liz Waid and Mike Procter look at koalas from Australia. People love these small, furry grey animals, but koalas are in danger.
Mike Procter and Liz Waid tell about clockmaker John Harrison. He invented a way for ships to know their East-West position at sea.