Overdeveloped body-parts slash Homosexual intercourse in an imitation of Star Trek sm Sadomasochism, pain for the pleasure of both. Killing which is supposed to arouse you. The author intended it simply to arouse. Mutually consensual adultery. Sex with food.
Participants are young.
Caring and consensual relationships between humans and animals. This is rape in law, but the style may be different. Woman says no, but loves it when she is raped. Nothing forces writers to use these codes, and many make up their own. But these are a start.