What joke is it to hurt a bowl of noodle soup? What's so funny?

Once upon a time, there was a mountain with a nun and a temple. Stay together. Because of the long-term love, the teacher and the abbot fell in love and were crazy about it, so they got that. But for fear of being discovered, the old monk thought of a clever plan for a day: he chiseled a hole in the kitchen wall. Then he said to the nun: As soon as I call Dong, you take off your pants and face this hole. In this way, they live well under the nourishment of love. One day, the old monk went down the mountain to do business. One of his disciples always wondered why the master shouted from the east as soon as he entered the kitchen. So he was curious and shouted "Out of the East". He didn't find anything special, so he ate below. Suddenly, he found a mouse in a solid hole. He picked up a spoon and poured boiling water into the hole. Right in the middle of the old nun. Well, the old nun has a bad voice, too. She silently endured severe pain. Soon after she went back to recuperate, the old monk came back and hurried to the kitchen. Before entering the door, she shouted "Out of the East Gate" and didn't see the old nun until she went in. He shouted a few times before he heard the old nun say that he was "burned by hair". The old monk asked. "Why does soup hurt?" The old nun replied slowly, "A bowl of noodle soup" and "How is the injury?" "lighter than hair!"