Grandma is joking and humorous.

This joke is a famous joke in A Dream of Red Mansions. It is usually used to describe someone who can eat very much and has a big appetite.

The meaning of this joke can be explained from two aspects:

First of all, this joke uses an exaggerated and absurd technique, and creates a humorous effect by describing "Lao Liu" as a person who can eat a cow and a whole old sow in one breath. This kind of exaggeration is very common in traditional jokes and comedies in China, which can attract people's attention and laughter.

Secondly, this joke also implies a satire on human nature and a criticism of society. In A Dream of Red Mansions, Granny Liu is a typical countryman, and her poverty, vulgarity and gluttony are vividly portrayed. This joke implies her insatiable greed and material desire by exaggerating her appetite. At the same time, it also reflected the differences of social classes at that time and the huge gap between rich families and poor farmers. Therefore, the meaning of this joke contains both humor and exaggeration, as well as profound social satire.