The 40th chapter of A Dream of Red Mansions specifically explains the function of the servant girl changing back into chopsticks.

It turned out that Granny Liu's pair of old square ivory chopsticks inlaid with gold was deliberately put in front of her by Feng to let her eat a plate of pigeon eggs, just to see Granny Liu's jokes. The result really amused everyone, from the Jia family, Mrs. Wang to the maid's daughter-in-law

According to the book, everyone was not interested in eating, but looked at him and made fun of him. At this time, Jia said that he would change a pair of chopsticks. Jia means that she has had enough fun. It's time to stop. She can't keep laughing here. She still wanted to eat. Anyway, Granny Liu was old, so she made way for everyone and everyone stopped.