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. Not only is Lake Victoria the largest lake in Africa, it is the second-largest freshwater lake in terms of area in the world. Bordered by Uganda, Kenya and Tanzania, it supports a diverse ecosystem of reefs and islands, including many unique species of fish. Lake Victoria is also one of the sources of the Nile River.