Walking towards the entrance of the mall this time of year incites feelings both thrilling and dreadful. It’s not the promise of mind-boggling sales or a free gift with purchase, but rather the instant replay in my mind of every great horror story set inside of one of America’s most sacred spaces (including Mannequin).

This replay typically starts of course with George A. Romero’s Dawn of the Dead, filmed just a few miles from my former home in Pittsburgh at the Monroeville Mall (there used to be a little museum inside with all kinds of memorabilia, but it’s now relocated to Evan’s City where Night of the Living Dead was shot). Holiday shoppers morph into hordes of zombies in my mind, stalking their way through the aisles with nothing but BRAINS on their minds... The reminder of Romero’s zombies makes the whole experience a little more tolerable, that is, until the horde reaches critical mass and tragedy feels imminent. That’s when I head to the roof and get the heck out.

There’s a lot to fear in crowds. As a sociologist, I find the science of crowds not only endlessly fascinating, but incredibly important to research and understand in order to save lives. About 12% of the US population will struggle with social phobia at some point in their life. For them, the idea of walking into a crowded mall full of eyes ready to judge can feel like torture (though some very cool VR exposure therapy is helping). But besides the fears we may bring with us, there are some very real threats lurking inside our sacred retail outlets, namely the crowd crush.

The terror of crowd crush made the mainstream headlines after the tragic, and worst single building fire to date, at the Iroquois Theatre in Chicago on December 30th, 1903. Around 2,000 people had gathered to watch a performance of Mr. Bluebeard, a combination burlesque and physical comedy show. About halfway through the performance, one of the arch lights set fire to a curtain. The fire quickly spread, eventually engulfing the entire theatre. Patrons began to flee in all directions, but sadly the building was working against them and an estimated 602 people died.

First there were the locked doors. Theatre officials didn’t want anyone sneaking in without paying. Yet, even if the doors had been unlocked, people couldn’t find them—they were covered by drapes with no exit signs in sight. What guests did find were ornamental doors, in front of which 200 people died trying to open. The doors that did open were narrow and, even more critically, they opened inward. The more people pushed, the less they could pull.

After the theatre fire made the headlines, people panicked. In the early 1900s, cities were growing faster than construction could safely keep up. Massive buildings were built without oversight or any kind of systemic regulation. Fear of disaster was real and it didn’t discriminate, from rich to poor, Americans were preoccupied with “what happens if…” when walking into a crowded space. Engineers, social scientists, and architects quickly went to work finding solutions, and their efforts have left us with safer spaces and a better understanding of crowd behavior.

Today we know that most crowds are not typically violent, and unlike the hordes of zombies in Dawn of the Dead, they’re not mindless or irrational. In fact, when people enter into crowds, we tend to reorganize ourselves into groups, even if these groups include strangers. Think about the last time you were exiting a concert, or one of the big amusement parks at closing. You look around and assess who’s with you, and become a kind of mini-unit.

I have observed this in my own research consulting for attractions: as a group moves through a space together—say from the parking lot, to a shuttle, to ticketing line—consciously or not a leader is identified, and a kind of collective awareness that you all move together emerges. Without going into detail, let’s just say I’ve seen over 20 people waiting in line for a Porta-John thinking it was for an attraction because that’s where their leader had gone. Again, groups like this are not mindless, rather they’ve ceded their decision making and movement to the group. Researchers call this self-categorization, and it happens everywhere: waiting outside for the doors to a venue to open, political rallies, and after natural disasters and threats to the public. It’s actually pretty cool, and studies show that when tragedy does strike, we help each other. We’re in this together.

So why, then, do crowds collapse? It’s terrifying to consider, let alone experience. Headlines usually use words like “stampede,” but typically it’s the exact opposite movement that leads to death. It starts with one person slipping or tripping in the front, and like a line of dominos, people fall one after the other. This is what happened at the Bethnal Green Crowd Crush in East London in 1943, and turned out to be the biggest single loss of civilian life during WWII. As sirens warned of a bombing raid, thousands rushed to the Tube Station for shelter. A mother, carrying her infant in her arms, slipped and fell, and from there the bodies piled up, leaving 173 dead.  Miraculously, her infant survived.

It’s not just the fall, though. When crowds reach a certain density, specifically when there are over six people per square meter, the chance for real danger is high. At this density we can no longer move of our own free will, we very literally are at the will of the crowd, namely the back of the crowd. Unaware of what is happening at the front, those in the back continue funneling in, assuming the forward momentum is a sign of progress, and so they keep moving. This was the case during England’s Victoria Hall Stampede in 1883 that left 183 kids dead. After a variety show, the children rushed down a staircase to the stage to get what was described as “The Greatest Prize There Ever Was.” Bodies quickly piled up at the bottom of a stairway where there was one door that opened inward. Artists sketched horrific images of the pile of children’s bodies, raising public outrage and leading to the development of the quick release escape bar (though not in time for the Iroquois theater).

The images of pile-ups are truly the stuff of horror movies, but there is another terror lurking in the midst of the crowd—the silent suffocation, or compressional asphyxia. Think of an escalator continuing to deliver people up to a platform with no place left to go. Or the nightmare for many performers: excited fans pushing their way to the front, their excitement quickly dissolving into terror as they find themselves suffocating against the weight of the crowd crushing on all sides. Only after the show is down and the pressure is off do people realize the collapsed bodies around them.

New technology, better planning in crowd control and flow, and very cool simulation programs are making these preventable disasters a thing of the past.  I look forward to the day we’re only talking about fictionalized accounts, perhaps deconstructing a horror movie that uses a crowd collapse as a means of reminding us just how connected we all are, and how much we depend on each other. Sounds like a perfect holiday horror movie to me.