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.
Quick Answer. The largest freshwater lake in the world by volume is Lake Baikal in Siberia. Its deepest point is 1,637 meters and it holds about 20 percent of the world's fresh surface water. The largest freshwater lake by surface area is Lake Superior.