Why do you call going to the toilet singing when traveling? >?

Originated from a joke, children often say that I have to pee when eating at home, and once grandma took her grandson to a high-end party. In order not to be rude, she taught the children to say, "If you have to pee when eating out, just say grandma I want to sing." Grandson remembered and successfully attended the party. Everyone fell asleep at night, and the grandson said eagerly, "Grandma, I want to sing." Grandma, I want to sing. "What do you want to sing in the middle of the night?" Grandma said, "I can't hold back, but I want to sing." Grandma can't say, "Then sing in grandma's ear, but in a low voice." . . . . .

One person is called solo, two people are called duet, more than three people are called chorus, and the roadside in the mountain is called folk song.