Both “erotica” and “horror” are emotional terms, referring not to any physical actions, but to emotional states. Erotica is specifically art intended to arouse physical desire. Although there are certain physical responses that are a part of this reaction, the reaction itself occurs in the minds of the audience. Horror as a genre is specifically referring to the capacity to instill fear, revulsion, or even terror into the audience. This is something to keep in mind when writing in either genre, because all too often writers and artists seem to focus entirely on the physical elements.
In purely visual mediums, this is understandable. A painting or picture can only do so much to do the things necessary to fully bring the viewer along for a journey. A simple portrait or picture of a nude man or woman might well be all that is required to achieve the intended reaction, but even in such cases there is usually effort made by the artist to convey something other than the pure physical form. Compare nudes sketches or photos that are done for the purposes of simply showing anatomy, versus works designed to arouse. The former is typically informative, but essentially unarousing. The latter is typically much more arousing, and this is due in large part to the emotional information conveyed by the work in question.
Faces in anatomical works are usually blank, neutral, conveying nothing about the subject except perhaps indifference. Faces in erotic works are typically full of various emotional reactions, and this is precisely because that emotional quality is essential to arouse the audience. Humans can be aroused by sheer anatomical close-up visuals, but typically they are aroused to much greater extents when emotions are involved in the work. A naked woman with a completely neutral face and posture isn’t going to do all that much for most male viewers, but add a bit of flush to the cheeks, a bit of a wanton smile, and suddenly any eroticism is greatly multiplied.
Humans are social creatures, and we as a species are typically concerned with and affected by the emotions that we see (or project) onto the people around us.
Most commonly, we are sexually aroused by seeing the emotion of sexual arousal in others. That flush to the cheeks can indicate a host of emotions that we associate with sex, from lust to embarrassment, to the kinds of physical exertion that we associate with enthusiastic sexual activity. As a hetero male, seeing art portraying an emotionally neutral naked woman provokes a certain level of arousal, a low-level spark of lust. Seeing art portraying a clothed (or partially clothed!) woman who’s looking at me (or another person in the art itself) with lust in her eyes, in her smile, in her flush, in her posture, can turn that spark into a bonfire.
Horror works the same way, although typically with different emotions (barring various kinks and phobias).
Picture a person being stabbed in the chest with a large knife, but with their countenance conveying complete indifference. Picture their limbs lying neutral. Picture their mouth closed in a lazy line, their eyes half-lidded with a lack of any interest.
Now picture the same stabbing, only with the target’s eyes wide with shock and fear, their mouth forced open by their scream of not only agony, but their understanding that these are their last moments of life, and that those last moments will be filled with suffering. Picture their legs buckling, their arms desperately failing to stop the incoming attack.
Neither of these images is necessarily going to instill you with fear, revulsion, or terror, but surely the second image comes closer to any of those emotions, comes closer to conveying horror, comes closer to doing the primary job that horror as a genre is designed for.
Let’s repeat the experiment with an erotic scene instead.
Picture a naked man and a naked woman. The woman is bent over a table, and the man is standing behind her. He is frozen mid-thrust, his cock half-way into (or out of) her. Their faces are blank masks, and their postures convey no urgency, no desire, and nothing about any kind of internal feeling about the act they’re in the middle of.
Re-imagine the scene.
This time, the woman is wearing a house dress. She is leaning over a kitchen table that has a cutting board with a knife and vegetables on it, as if she has been interrupted in the middle of preparing a meal. Picture her hands bunching the checkered tablecloth. Picture her face flushed with passion, her eyes closed with pleasure, her mouth opening wide with a moan of ecstasy. The top of her dress has been pulled down, exposing her bare breasts. The bottom of her dress has been lifted up, and her panties pushed aside so that the man could eagerly penetrate her.
He’s wearing slightly shabby clothing, as if he’s been working in the yard, and only came in for a break or a drink of water. His hands are on her hips, frozen in the act of frantically pulling her back against him. His eyes are filled with lust, his face red with it. His pants are unzipped and have been pulled down just enough for this spontaneous act of mutual passion.
Stereotypical gender roles aside (or especially included, depending on one’s kinks), which scene was more arousing?
Most likely the latter, because the characters we see in a work of art are our vehicle for this experience, our avatars and objects of desire. If we can see passion, we can feel that passion. Just as if we see fear or pain, we can experience that as well.
It’s the same in written work: a story must be about more than indifferent bodies in order to truly affect the reader. The characters must feel emotions, and these emotions must be transmitted to the readers in order to infect them with the appropriate feelings of fear or desire.
The goal of most art is to affect the audience somehow, and that’s incredibly difficult and rare to do without showing them any emotions within the art itself. Emotions are the key to affecting your readers, and details are the key to showing emotions.