One day in class, the teacher asked the students why cows eat grass. Everyone started answering in their own way—some said that cows' favorite food is grass, some said that it gives them energy. Suddenly, a student said jokingly that since childhood, he had seen that the mother of a cow also eats grass, so the cow also eats that. His simple answer made the whole class burst into laughter. The teacher also smiled and explained that in fact cows are herbivores, so grass is the main part of their diet. This small incident teaches us that sometimes simple and straightforward thoughts give us joy and make the learning process more beautiful.