What was the nozzle when the model was made? How to avoid it

Shuikou is a little plastic left on the surface of the model after the model is cut from the "runner", commonly known as Shuikou.

The way to deal with the nozzle is to cut it as short as possible with a pen and knife, but don't cut it all off, because it is easy to hurt the parts. The rest is slowly polished off with sandpaper. Sandpaper is first polished with about 800 #, and then polished with sandpaper to make the surface of the parts very smooth.