Recently I've fallen in love with a horror game I've never even played. It's called Five Nights at Freddy's, and I discovered it through a series of YouTube videos. I watched as four to five players sat down at their PCs and started from the same point in the game. All I could see were their faces. Their brows furrowed, their faces wrinkled as they winced at false jump-scares, their hands flew over their mouths when some terrifying animatronic popped out and killed them—and I did all the same things along with them. I could feel the anxiety showing on their faces. I felt the weird excitement and exhilaration they got from being scared, even though I never saw a single frame of Five Nights. The videos were so much fun that I wanted more. But I didn't download the game. Instead, I searched for more videos of people reacting to things.

Videos of people reacting to games—or commercials, or the deaths of legendary pop stars, or old-school computer software—are incredibly popular online. Lots of people make them, but the reigning champs are comedy duo Fine Brothers. Their various YouTube channels have over 20 million subscribers, and their channel devoted to nothing but reaction videos—simply titled "React"—has over 903 million views.

Recently the Fine Bros got into hot water when they tried to trademark the word "react". It was part of their React World project, in which people pay the duo to create reaction videos. The backlash was swift and loud, and the Fine Bros backed off. Too many people are invested in making their own react videos to allow just one pair of creators to own the idea. React videos have tapped into some part of our nature that relishes watching other people experience stuff.

The (possible) mirror in our brains

We could explain away the popularity of these videos as #youths being #youths and leave it at that. But science has a deeper explanation that might have to do with empathy and what are called "mirror" neurons.

In the 1990s, a group of Italian researchers discovered that when a macaque monkey reaches for food, certain neurons light up in its brain. Those same neurons light up when the monkey sees a human reach for food, too. Later named mirror neurons, some believe these cells are active in human brains as well, but their existence is controversial. Some studies question if they are present in the human brain at all, while others have found evidence of their activity but can't say for sure how they work in humans.

If mirror neurons do exist and contribute to our emotions, they could explain why we get anxious when we see someone else get anxious. USC neuroscientist Lisa Aziz-Zadeh told Ars via email that mirror neurons could be one reason why we enjoy watching other people do things, like trying to stifle uncontrollable laughter or playing Star Wars: Battlefront for the first time. "Mirror neurons are active both when you pick up a cup and when you see someone else pick up a cup," says Dr. Aziz-Zadeh. "As mirror neurons support a system that could simulate other people's actions onto one's own motor representations, it is thought that they contribute to social understanding."

Mirror neurons could explain why we feel empathy. "By putting 'self' and 'other' on the same neural architecture, it has been postulated to be a neural architecture which may support social understanding and contribute to empathic processing," Aziz-Zadeh says. "But other brain regions are probably involved as well."

Bingeing on emotions

Empathy may be another reason react videos are so easy to watch. Most viral things on the Internet are easily digested, either due to subject matter (the sillier the better) or duration (the shorter the better). React videos are neither the shortest videos online nor are their topics always funny. Instead, their digestibility comes from recognizable emotion.

Andrea Weinstein, a clinical psychologist and psychology doctoral intern at the San Francisco VA Medical Center, told Ars that as social creatures, humans crave understandable emotions because that's how we create social bonds. "I would imagine when we're watching people react, it's such an easy-to-translate response," Weinstein says. "When you watch someone react to something with a big response, it's much easier to empathize with them because you know exactly what they're feeling."

We've all had passive-aggressive friends who are difficult to be around because we can't read them. Unrecognizable emotion is just one way social bonds break down. In turn, clear emotions help us relate to other people, even strangers on a computer screen. "We feel immediately bonded to them because we say, 'Yep, I would have that reaction, too'," Weinstein says. "You feel like you've been heard in some way because you've bonded with them." React videos provide a two-fold experience: we feel satisfied because we know the emotions being conveyed in the video, and we bond with the reactor because we can share their emotions.

Maybe that's why we can so easily forgo work and responsibilities and fall into a YouTube binge-watching hole. Take my personal Five Nights at Freddy's experience: I had already created a social bond with the people in the first video, and I got scared by the game along with them. Of course I wanted to keep watching after that. They understood me and I understood them... they just got me.

“Hey, you're just like me!”

This is what I like to call the "just like me" factor. This is why, in addition to react videos, we love watching proposal videos or watching someone spectacularly wipe out—and why we cry and cringe while doing so. We see ourselves in the person being recorded, and we empathize. Weinstein describes this feeling as "mutual knowing." Many YouTube sub-communities base their existence on the "just like me" factor.

React videos are only one genre of video that has a hardcore following—gaming and beauty also attract huge communities loyal to those creators and the videos they produce. That "you're just like me" feeling you get when you watch a react video is similar to what a gamer feels when he or she watches a video of PewDiePie stumble through Best Horror Game Ever (?).

So while we might not be able to fully understand where empathetic feelings come from in our brains, we can say that something in our heads gets triggered when we relate to someone else. In a way, YouTube is based on that feeling—many of the most popular YouTube creators are those that viewers can relate to the most, whether it's due to age, gender, sense of humor, or passions. As online video continues to grow, that feeling of familiarity will be what keeps react-style videos around for the long haul.

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