NSFL stands for Not Safe For Life. While NSFW covers things that are generally considered socially acceptable in private situations, but inappropriate for more public or formal situations, NSFL is for stuff that could be traumatizing or deeply disturbing, even in a private context.
Stuff like extreme violence or abuse can be more obvious examples of NSFL, but stuff like scat is more of a gray (well, gray-ish brown) area.
Ultimately, the issue is that this place needs a more sophisticated filtering system.