Good horror is written by people who understand that fear is one of the cardinal passageways into the core of humanity. Good horror is generally written by folks who grew up on horror; books, movies, etc. You can’t simply decide to write—in any genre—if you don’t first have an understanding of the topic and a strong mental backlog of reference.
Yep,” I said, rolling the body onto its back and staring into the horrified, bloated face, “you’re a single-bagger. My kinda gal.” I gave her a smile and a friendly wink. The face stared back at me with that same frozen look of terror. “Oh, stop being so dramatic,” I said, “You’ll be pretty again, I promise.