If you think you’ve outgrown fairy tales, it might be time to think again.

It’s true that many fairy tales include fanciful, magical beings―not just fairies but also dragons, elves, giants, and witches. And the heroes of these stories are often royals―princesses and princes, queens and kings.

These elements may sound familiar and comforting, but the original versions of the fairy tales you remember weren’t likely to soothe young children to sleep. Instead, they would have scared them silly.

You’re probably more familiar with the Disney versions of fairy tales. The company bases many of its G-rated movies on popular stories that are hundreds of years old. The Little Mermaid, for example, is a Danish fairy tale that dates back to the 1800s: A young mermaid falls for a human prince and gives up everything she loves, including her beautiful, powerful tail, to be with him. In the Disney version, the two live happily ever after. Sounds sweet and romantic, doesn’t it?

What was the story like when it was first written down? In the version published by Hans Christian Andersen in 1837, the mermaid asks a witch to help her convince a human prince to love her. The witch agrees, but as part of the deal, the mermaid must trade her flipper for human legs. According to Andersen’s version, the mermaid feels as though she is walking on sharp knives. Her legs ache and bleed constantly. And there’s another catch: If the prince marries someone else, the mermaid will die of a broken heart and dissolve into sea foam.

Unfortunately for the little mermaid, the prince is already in love with someone else and does indeed marry that woman. In her despair, the mermaid learns that there is one way that she can yet survive: to save herself, she can kill the prince and let his blood drip onto her feet. The little mermaid cannot bring herself to do this, however, and chooses her own death instead.

It’s a pretty dark and grisly story, isn’t it? The original versions of most fairy tales were quite horrific. They would likely earn an R rating if produced in their original forms.

In the original “Cinderella,” the evil stepsisters cut off their toes and heels to make the slipper fit so that they can marry the prince. And at the end of that story, doves peck out their eyes.

Why would a culture produce such gruesome lore? And why would those stories survive for hundreds of years? The first reason is a familiar one: even today, people love the thrill of a scary story! The details in the original versions of fairy tales were not easy to forget.

But here’s another, perhaps more important reason: Fairy tales and folk tales were meant to send messages about how people in a society should behave. Fairy tales often showed the tragic consequences of a choice that was considered foolish, selfish, or careless by the culture that created the story. The details were harsh, to make sure that the story would stay with listeners forever.

The next time you want a really scary story, try to find the original version of your favorite fairy tale. You just might have to leave the lights on!