"Prince Qing Yu, you flatter me too much. I haven't even fully grasped it myself, how could I possibly teach a disciple?" Lin Shen said with a smile, "If Prince Qing Yu needs, we can exchange knowledge through sparring. To be your master, I am truly unqualified."
How could Lin Shen teach her Finger Sand? To practice Finger Sand, one must base it on the Twenty-Eight Fists and the Thousand Men's Pointer. The origins of both skills were problematic. The Twenty-Eight Fists could be taught to others, but the Thousand Men's Pointer absolutely must not be casually disseminated.
The hidden skill, Heart Concealment, was even acquired from Red Heart A, which made it all the more taboo to reveal. If discovered by Red Heart A, there would likely be serious trouble.