2. Although boiled in boiling water, the residues of pesticides and toxins will more or less adhere to the surface of green beans, and the toxins and pesticide residues on the surface will be further washed away with cold water.

3. Green beans will swell after blanching at high temperature. If the time is not well controlled for a long time, the green beans will "ooze" (that is, they are cooked too well, which means they taste bad). After being cooled with cold water, the meat will become tight and crisp after expanding with heat and contracting with cold.