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.
The most important lake area in Africa is undoubtedly that of the Great Lakes. The African Great Lakes are a series of lakes constituting the part of the Rift Valley lakes in and around the East African Rift. They include Lake Malawi (or Lake Nyasa), with over 500 endemic fish species, and Lake Victoria.