How ice in cold sky water can make more ice and why that's important

I want to explain a thing that happens in cold sky water. By cold sky water I mean the white or sometimes grey things we see above us that make rain or cold, white, hard rain. When it is cold but not very cold, the cold sky water can be made out of wet water or ice. Often the cold sky water is made out of both wet water and ice. The wet water would also like to be ice, because it is cold. But the wet water needs something to begin making it to ice. This something are very small things in the air. But not all small things in the air make wet water into ice. And this works better when it is colder (but not very cold, then wet water can become ice without the small things). When we look at the very small things and ice in the same air that is cold but not very cold, we often see many more ice than small things that make wet water into ice. That seems strange. But we can explain this with a bright idea. What if ice can make more ice without the small things that make wet water into ice. That can happen when ice hits other ice and small ice breaks off but also in other ways. In my up-goer five talk, I want to explain this idea more and talk about how I look into this second way to make ice in cold sky water in the land of the ice.