Why did the bullfrog suddenly say "mom"?

Bullfrog: It called itself, so it got its name, because it called like a cow. The vocal cords of this Taizhou bullfrog, which sounds like a baby mother, may have changed during feeding. Liu Jiaoshou further metaphor, people's voices vary widely, some thick, some thin, bullfrog. The shrill cry of this bullfrog is just close to the baby's cry, which sounds like calling for our mother, and it incorporates our subjective "assumptions".

Further talk about bullfrog: Bullfrog is native to North America, and it is named after its loud voice resembling Niu Jiao. Bullfrog was introduced into China from Cuba in 1959, and was widely cultivated in China around 1990s. In recent years, bullfrog has become one of the important characteristic aquatic products in aquaculture in China.