Fear is a necessary human emotion. It alerts us to possible trouble so that we can react, which in turn helps us survive potentially deadly situations. When encountering danger, fear triggers us into fight-or-flight mode. We can either choose to go up against the perceived threat, or we can run away as fast as possible.

But there is another response… Freeze. When something just stops us in our tracks, and we make like Elsa in Frozen. Some of the signs pictured here have elicited that very response from the people who encountered them. Until they became unstuck enough to take a photograph and share it with the r/ScarySigns community.

If fear is a negative emotion and a state that many of us don't necessarily like being in, why do we enjoy watching horror movies, or scrolling through photos of terrifying signs? According to experts, it has something to do with the chemicals our body releases after being scared.

Margee Kerr has dedicated her career to learning as much about fear as she can. She’s a sociologist and the author of SCREAM: Chilling Adventures in the Science of Fear. She says fear floods our bodies with "feel-good" hormones. "Our arousal system is activated and triggers a cascade of 'feel good' neurotransmitters and hormones like endorphins, dopamine, serotonin, and adrenaline that influence our brains and our bodies," Kerr told The Huffington Post.

You’d most likely be watching a horror movie or scrolling through these pics in a place where you feel safe. Not while you’re in immediate, real danger. And that makes a big difference. “To really enjoy a scary situation, we have to know we’re in a safe environment,” Kerr told The Atlantic. “It’s all about triggering the amazing fight-or-flight response to experience the flood of adrenaline, endorphins, and dopamine, but in a completely safe space.”

Kerr says humans have been intentionally scaring themselves, and each other, since the dawn of time. "Through all kinds of methods like storytelling, jumping off cliffs, and popping out to startle each other from the recesses of some dark cave," she said.

The expert adds that there are various reasons for this. "To build group unity, to prepare kids for life in the scary world, and of course, to control behavior. But it's only really in the last few centuries that scaring ourselves for fun (and profit) has become a highly sought-after experience."

Sometimes we put ourselves into a state of fear purely just to "feel." "For many people everyday life can feel overly routinized and even boring," said Dr. David Zald, director of the Affective Neuroscience Laboratory at Vanderbilt University. "By contrast, when scared we are fully aware, conscious and in the moment. We are not preoccupied thinking about what happened yesterday or what we have to do tomorrow." Have you ever noticed how you feel wide awake after getting a fright? Now you know why.

Not everyone enjoys fear. Some actually have a fear of fear. According to VeryWellMind, “Whereas most people experience fear only during a situation that is perceived as scary or threatening, those who live with anxiety disorders may become afraid that they will experience a fear response. They perceive their fear responses as negative and go out of their way to avoid those responses.”