1. Preserved eggs cannot be eaten directly with vinegar. Because preserved eggs are alkaline foods, they will precipitate with calcium in vinegar, which is not easy to digest and may lead to poisoning in severe cases.

2. Preserved eggs can't be eaten with eel. Although preserved eggs are rich in protein, and Monopterus albus is also a nutritious and delicious food, because preserved eggs are alkaline food, eating them with Monopterus albus will lead to diarrhea and food poisoning.

3. Preserved eggs should not be eaten cold with brown sugar. Preserved eggs belong to alkaline food, brown sugar belongs to acidic food, preserved eggs and brown sugar are eaten together, and acid will merge with alkalinity, leading to acid-base imbalance. Therefore, the combination of brown sugar and preserved eggs will lead to stomach diseases and mild food poisoning. Similarly, preserved eggs can't be eaten with white sugar and rock sugar.

4. Preserved eggs should not be eaten with turtles and plums. Plums, soft-shelled turtles and preserved eggs are similar foods, and eating them at the same time can cause food poisoning, vomiting and other symptoms.