Fish without sheep is not fresh.

The word "food" means to be kind to others. Only kind people can succeed and get food.

Fish and sheep together are the word "fresh", which means that if there are sheep and fish in the diet, the dishes will be delicious.

The upper and lower couplets all use the structure of Chinese characters to reason, which not only connects the contents of diet and mutton restaurant, but also meets the requirements of antithesis. The word "food" and the word "fresh" are the sound of puckering and the sound of peace, respectively, and follow the principle of "puckering up and flattening down" in couplets.