The most convincing explanation is that when someone is finding it difficult to understand what is said to them, he/she engages in a form of lip-reading: he/she will observe the lips of the talker and mimic the talker's lip movements.
Lake Tanganyika is an African Great Lake. It is estimated to be the second largest freshwater lake in the world by volume, and the second deepest, in both cases, after only Lake Baikal in Siberia; it is also the world's longest freshwater lake.
Lake Victoria, Victoria Nyanza, a lake in East Africa, in Tanzania, Uganda, and Kenya, at an altitude of 1134 m (3720 ft): the largest lake in Africa and second largest in the world; drained by the Victoria Nile. Area: 69 485 sq km (26 828 sq miles)