2/3. Underworld. Charlotte Uhlenbroek's tropical trip brings her to the Congo, Africa's heart of darkness and home to some of the most deadly plants and animals, such as leeches and driver ants. Lowland gorillas, chimps and forest elephants forage here, but it's the lowlife on the forest floor that holds the secrets to life and death in the jungle. Director Nigel Pope ; Producer Karen Bass www.bbc.co.uk/nature