In the second episode of Old Princess Zhu Huan, which episode is about you in the dark?

In episode 37 of the second part, Xiao Jian wants to make a piano for Wei Zi after Wei Zi became blind. As soon as the swallow heard that the strings made of horse hair were the best, he pulled the ponytail to pull out the horse hair, and the horse punched and kicked him. After the piano performance, Wei Zi sang You in the Dark to express her experience in this period.