The next sentence of the postscript of "Pickled Vegetables and Braised Tofu" is "Salt" comes first.

It is a metaphor for stating conditions or rules before doing something. We are cooking with pickled vegetables and roasted tofu. As you say (salt) comes first, it’s totally fine for me to help you buy things this time, but if you don’t do it next time, don’t come to me again.

A quip, also called a witticism, is a short, humorous, lively and witty sentence that is loved by the masses. It consists of two parts: the front part is an image metaphor, which acts as a "lead", like a riddle; the back part is an explanation, like the answer to a riddle, which is particularly natural and appropriate. In a certain language environment, you often say the first half and "break" the second half, and then you can understand and guess its original meaning, so it is called "Xiehouyu".

Xiehouyu comes from a kind of "Xiehou style" in Tang poetry, which was created by Zheng Qi in the Tang Dynasty. There is an interesting anecdote in the "Old Book of Tang: Biography of Zheng Wei": Zheng Wei was good at writing poems, and there were always "thorns" in his poems, and the style of his poems was also a bit strange. At that time, it was called "Zheng Wu Xie Hou Style". This strange style of poetry, which was originally unappreciated, spread like wildfire and was widely circulated. Even Emperor Zhaozong of the Tang Dynasty always heard his subordinates recite it.

Many of these poems satirized current affairs, but Emperor Zhaozong of the Tang Dynasty, instead of being surprised, felt that the poems were very "connotative" and personally criticized "Zheng Xike, Minister of Rites, Ping Zhangshi". Later, Zheng Wei really became prime minister. However, after he became an official, he became taciturn and rarely wrote any barbed Xiehou poems, but the Xiehou style has been passed down since then.