1. Chewing gum while cutting onions prevents you from crying because the opening and closing of your mouth creates pressure, forcing excess tears into your mouth.

2. Bread contains starch crystals, and water is needed to form these starch crystals. This causes the gluten in the bread to lose water and become hard, which is why bread hardens if left out for a long time.

3. Cut lotus root slices will turn black because lotus root contains polyphenolic compounds, which will form melanin when exposed to air.

4. Drinking too much water can also cause poisoning. This is because drinking too much water can lead to excessive hydration in the body, resulting in a low concentration of sodium ions that cannot meet the body's needs, thus causing hyponatremia.

5. Water molecules have a main chain structure. If water is not in a flowing state, this main chain structure will expand and extend, and the water will become "aged" water, commonly known as dead water.

6. In 2010, scientists turned water at 20°C into ice. This was because applying an electric field to the water increased the atmospheric pressure, raising the freezing point of the water and making it easier to freeze.

7. Hot water is more effective at extinguishing fires because hot water will quickly vaporize when it comes into contact with high temperatures, producing water vapor that covers the burning material, preventing it from coming into contact with oxygen and thus preventing complete combustion.

8. Water droplets bounce when they hit an iron plate because the high temperature causes the bottom of the droplet to vaporize rapidly, and the resulting water vapor carries the droplet around.

9. Milk will also thicken if left for a long time. This is because milk contains fat, and the density of fat particles is less than the overall density of milk. Over time, it will rise to the surface of the milk.

10. Orange juice tastes terrible after brushing your teeth. This is because the foaming agents and sodium lauryl ether sulfate in orange juice inhibit our sweet taste receptors, while also increasing our sensitivity to bitterness, making the orange juice taste awful.

11. Chocolate first appeared in the Aztecs of Mexico as a beverage with a bitter and spicy taste.

12. Bottled beverages are never completely full because of the principle of thermal expansion and contraction. If the beverage expands when heated, it will cause the bottle to deform and burst. Moreover, many beverages are carbonated drinks, which will generate carbon dioxide gas with slight shaking. If the bottle is too full, it is more likely to burst.

13. The freezer compartment of the refrigerator has no light because the temperature in the freezer compartment is too low. When the light is turned on, it will heat up, and the resulting temperature difference will cause the light to explode.

14. Radiators are always installed near windows because they can quickly heat the cold air entering the room, creating a circulation system of hot air flow. If radiators are installed elsewhere, the cold air will occupy most of the room first and will only be heated when it encounters the radiator, which will greatly reduce the efficiency of the heating system.

15. During the day, the windows appear dark because most of the light enters the room, and only a small amount of light enters our eyes.

16. When a magnet is heated, the arrangement of atoms inside the magnet changes under the influence of high temperature, thereby reducing some of the magnetism.

17. In 1506, a hand scroll from Nuremberg, Germany, contained a drawing of a lighter, while matches were not invented until 1852.

18. Solar heaters should be tilted to form a right angle with the light so as to collect solar energy to the maximum extent.

19. Straws are cylindrical because, for the same circumference, the area of ​​a circle is larger than that of other geometric shapes, allowing you to drink more. Also, a cylinder has greater support and is not easily bent. Finally, the shape of a cylinder feels comfortable to the touch.

20. The reason why plastic wrap sticks tightly to the ceramic plate is that when the plastic wrap is stretched, it becomes static electricity, creating a potential difference between the plastic wrap and the plate, thus causing it to stick tightly to the plate.

21. Flames come in many colors, which are related to the components that are burning. For example, phosphorus burns green, while sodium burns yellow.