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.
2Lake Tanganyika (4,710 feet [1,436 meters]) Â© Blossfeldia/Dreamstime.com Lake Tanganyika is the second largest freshwater lake in the world and the second deepest lake of any kind. It sits on the border between Zambia, Burundi, Tanzania, and the Democratic Republic of the Congo.