What is "Shuikou"?

The nozzle is the little plastic left on the surface of the model after cutting it off from the "runner", commonly known as the nozzle.

The way to deal with the nozzle is to use a pen knife to cut it as short as possible, but do not cut it all off, because it is easy to damage the parts.

Slowly sand off the remaining bit with sandpaper. First smooth it with about 800 grit sandpaper, and then hit it with polishing sandpaper, so that the surface of the part will be very smooth.

You will understand after trying it a few times.