Have you noticed that the toilet seat in the public toilet is a little different from the toilet seat at home? Unless someone points it out to you, you may miss it. The next time you go to the public toilet, look at it before sitting down. You will not encounter ellipses or circles, but incomplete things

Common toilet seat has PP and UF (duroplast) two kinds of material.

Many people are not used to close the toilet seat, the author suggests that you must cover the toilet before the toilet flush.