Sex zombies are a disturbing is rather harmless phenomena. Some spirits are so passionate for each other that their bodies re-enact their love. The corpses animate and move heaven and earth to get together generally leaving quite a mess. Once together they continue their love making till rot and friction destroys the last of their material form. Some of the more odd members of psychic community arrange views of sex zombies in action for necrophiliac voyeurs. It's a profitable if not respectable business.
This was something you needed to know, but probably should never see.