Why do the rich say that raising pigs is like a mountain, and the mouse's head dies?

Because couplets are pronounced differently.

Reading of the rich:

Raise a pig like a mountain, and the mouse will die.

A good wine jar makes the vinegar jar sour.

And the correct pronunciation of this couplet is:

Raising pigs is as big as a mountain mouse, and its head is dead.

Wine vats are good for vinegar, but the jar is sour.

This couplet is used to satirize the rich.

Extended information This is a usage of couplets, that is, irony, and it is also a method that many ancient people like to use, such as:

Yu Qian in Ming dynasty

When Yu Qian was a child, he wore two braids on his head and played in the street. Suddenly, a monk came, met Yu Qian, laughed and sarcastically said, "The ox head is happy and the dragon horn is born." It means that Yu Qian is a little stupid cow, and only two braids have a future.

Xiao Yuqian is really puzzled: "Why is this monk mocking me?" However, Yu Qian was very talented. He said unhurriedly, "Did a dog ever have ivory in its mouth?" When the monk heard this couplet, his face changed immediately. The problem is that he spoke defiantly first, and Yu Qian's bottom line was neat. He had nothing to say and left despondently.