What is the meaning Zen riddle?

The most famous Zen riddle appeared in the Platform Sutra (六祖檀經). When young Shen Hui (神會 - who later became one of his master's most famous students) at age 13 first went to see the sixth Patriarch  Hui Neng (慧能). Young Shen Hui was smart, knowledgeable (on Buddhist Sutra) and arrogant. Hui Neng asked (I paraphrase):

"If I hit you with a stick, do you feel pain or no pain? If you do not feel pain, you are heartless and useless as as piece of cold stone, and if you feel pain, you have planned the seed of revengeful grudge."

Shen Hui was immediately enlightened, and he became his master's faithful student from that moment onwards.

How to solve this riddle? And what did young Shen Hui learned? Young Shen Hui was transformed from a wild and highly intelligent young prodigy into (the beginning of) a humble monk for the rest of his life. I have no way to ask the dead!

Recently I found a similar riddle that perhaps may shed some lights into solving this riddle. It was from a book written by the a Taoist named Liu Ming Rui (劉名瑞), master of Zhao Bi-Chen (趙壁塵) the author of the famous book Taoist Yoga translated by Zen master Charles Luk. All his writings were recently republished in China under the name of "The complete works of the Knocking-sandles-Taoist" 敲蹻道人全集. I shall make more comments of his brilliant works in my future posts.  Here, I would only like to quote a Zen riddle from the first part of his Knccking-sandles-Cave-work ( 敲蹻洞章）.

The story runs like this: In the past there was a (Buddhist) monk who was supported by a respectable royalty who provided the monk with a place where he could practice Zen meditation undisturbed. He also provided the monk with food and clothing, a place to sleep with medical and other provisions. And his support lasted for years. One day, he secretly sent one of his young slave girls to test the monk through seduction. The monk was not moved. The slave girl commented: the monk was like dead wood and cold rock, as cold as three winters with no heat. Hearing this, the respectable royalty concluded that the monk was not enlightened after all these years of practice. And he dismissed the monk.

My dear reader, you might wonder why. Had the monk succumbed to the slave girl's seduction, the respectable royalty should have also dismissed the monk. What should the monk do?

My dear reader, and what should young Shen Hui do: pain or no pain?

The complete works of Liu Ming Rui - Master of Zhao Bi-Chen (author of Taoist Yoga)