I think you misunderstood the meaning of that chapter. If I remember correctly, it should be: weak bones and soft muscles but strong grip. Unknown combination of oysters. Extremely refined. Let me explain it to you based on my understanding: It means that although the child's muscles and bones are weak, he can hold his fist very tightly. Although he doesn't know about sex between men and women, he can get hard down there. This is because he is full of energy. That's probably what it means.