Zombies are the monsters of the 21st century, and America's major contribution to horror. What set off zombie fever? All roads lead to George Romero, who made zombies a metaphor for social ills.

Slashers got sophisticated in the '90s, evolving from Freddy Krueger to Candyman to the terrifying Hannibal Lector. The 2000s brought "torture porn" – a response to post-9/11 panic.

The fear that demons will enter our bodies and make us do terrible things has inspired some of the most frightening films ever made, including the masterpieces Rosemary's Baby and The Exorcist.

The history of monster movies is also the history of the evolution of special effects technology; whatever their size or shape and whatever they represent, for many horror fans monsters are the best part of the genre.

Nine Nightmares is a deep dive into nine uncategorizable films that push the boundaries of horror. Great films that entertain us and provoke us. Films that put society under a microscope, making us question not just what we fear, but why we fear it.

Fans of horror films, like "A Nightmare on Elm Street 3," "Psycho II," "The First Purge," "Bride of Chucky," "Scream 2" and "Gremlins 2: The New Batch," say sometimes sequels are as good or even better than the originals.