Why did the old man say, "Three or nine days opened up"?

Three or nine days have opened up, and old people and old ladies are afraid. Why do you say that? There is a certain reason for this:

March 9 is supposed to be the coldest period in a year, but it is not cold, but also frozen. Suddenly, the weather changes greatly, and the resistance of the old man and the old woman has decreased, so they are very sensitive to the outside weather, so they will catch a cold and have a fever, and of course they are afraid of such weather!

So, it's a big day, and old people and old ladies are afraid. That's fear of catching a cold!