The Haunting is one of cinema's spookiest. But thinking back on the scares, you might remember that the spine-tingling sequences are missing something – a visible shock.

As Director Robert Wise said, “You see nothing. You can’t see a cold spot.”

Wise’s masterpiece expertly relies on suggestions to create the feeling that one sees more than they actually are.

When adapting the story, screenwriter Nelson Gidding had his own "a-ha" moment after examining the lead character’s narrative arc.

“This isn’t a ghost story at all. It’s about a woman who is having a nervous breakdown," he said.

So for him, the haunted house was a manifestation of a sanitarium, the paranormal investigator was a doctor, and Theo was a nurse.

“I understand that when you undergo shock treatment you feel very cold afterwards,” Gidding said. “And of course, the violence of the shock treatment itself is the noise and the banging of the haunted house.”

To accentuate this, Gidding removed any moments that took the action away from the home, such as a potential picnic scene. Instead, he wanted everything anchored to Hill House in order to create a claustrophobic feeling.

To ensure his interpretation of the story was right, however, Gidding and Wise went to the source: author Shirley Jackson.

Approximately four years before completing The Haunting of Hill House, Jackson wrote The Bird’s Nest, a novel about a woman with multiple personalities. So Gidding’s theory of a mental breakdown wasn’t coming out of left field. But was he correct?

While she appreciated his creativity and inventiveness, Jackson didn't intend for her story to be interpreted as such. 

“She was wonderful, a very smart woman,” Gidding recalled. “She was very gracious.”

In the end, Gidding decided to leave the film's ending up to the viewer.

He said, “I believe there could be such a thing as a haunted house. It could also be paranormal, and the things that happen will be explained someday.”