How did the ancient court test whether a maid-in-waiting was a virgin?

What is guarding the palace? In fact, the gecko is guarding the palace. The so-called guarding the palace means guarding the inner court of the palace. The emperor has at least three palaces and six courtyards. It is said that there are 3,000 beauties in the harem. These women belong to the emperor alone, and no one else can touch them. In order to prevent promiscuity in the palace, the inner prison will choose dark blue gecko, put it in a blue crock and keep it in a cool place. People feed these little geckos with cinnabar every day. After more than three years, the gecko in the green crock can weigh seven or eight pounds, which is quite big. They put it away, wrapped it in mulberry bags, dried it on cool tiles, crushed it and put it on the arm of a woman who had just entered the palace. From then on, there was a red spot on her arm called Gong Sha. Once a virgin loses her virginity, the palace sand will disappear, otherwise she will never retreat. In this way, the emperor restrained his woman. Once it is found that any unlucky woman has no palace sand on her arm, it is the crime of deceiving the monarch, and it is the sin of Yi Jiuzu to cuckold the emperor.