Twenty-eight refers to girls around the age of sixteen. Crispy means that these people's bodies are very delicate and will make people feel very happy during sexual contact. Secretly teaching you that your bone marrow is dry shows that you are addicted to this lust and your body will collapse unconsciously. The ancients regarded sperm as the product of human qi and blood. And qi and blood are produced by bone marrow. Excessive consumption of blood and bone marrow, and finally the whole person collapsed. So there is a saying that the bone marrow is dry. In fact, if you want to repeat the whole sentence simply, it should be interpreted as: although those beautiful young girls bring you a good impression, they will make you unconsciously collapse.