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

A child went to town with his grandmother. On the main road, the little grandson shouted, "Grandma, I need to go to the toilet."

Grandma said, "Shh, keep your voice down. We should be gentle in the city, and say that we want to sing when we go to the toilet.

Grandson said, "Oh, I want to sing, Grandma took her little grandson to the toilet."

At night, they went home, slept, and the little grandson wanted to pee again. He called Grandpa, "Grandpa, I want to sing." The sleeping grandfather heard Grandson.