Interpreting Women: Why do girls close their eyes slightly when kissing

A friend told me that he and his girlfriend had broken up. I asked him why, and he replied: "When we kissed, I found that she actually opened her eyes, and her eyes were no different from usual. How could I stand it?" I was stunned, and then couldn't help laughing out loud. He looked at me angrily, and I quickly said: "Sorry, I didn't mean to make fun of you. It's just that this answer is too unexpected."