Chilling footage shows high school students watching in stunned silence on September 11 2001 as they learn about the terrorist attack on the World Trade Center.
Students at a high school in Virginia were filming a class project and can initially be seen joking around with each other.
But the mood changes as they are then seen watching news footage of the 9/11 attack as it unfolds in real-time.
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One of the students quietly says, "Oh my gosh." Another holds his head in his hands.
The attack on the Twin Towers 22 years ago is one of the most deadly terrorist attacks in history, killing 2,977 people.
Back in 2001, most people learned of the devastating news together, whereas now most of us get breaking news alerts direct to our smartphones.
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This is partly what makes this clip of dumbfounded students in their classroom learning about the horrific attack even more upsetting.
Reacting to the footage, one person explained that they hadn't been born yet, writing: "I can’t imagine what it would [have] been like seeing it on TV."
"The chills. This isn’t something you can forget," said another, while a third wrote: "It felt like the world was ending!"
A fourth added: "I was in high school at that time too and remember how school ended and we were all glued to the TV. Crazy to see this."
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Another student similarly filmed the reaction of her roommate as they sat in their New York apartment and watched the scene unfolding in front of them.
Caroline Dries and her friend Megan were woken up by the first explosion and assumed it was a bomb that had been planted at the top of the building.
But shortly afterwards, the young women launch into panic as they see the second plane crashing into the neighbouring tower.
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Speaking to CNN in 2011, Caroline – who is now a successful TV writer and producer – said: "We were kids, like we were so vulnerable and so naïve.
"My reaction was 'there's no way people are going to be jumping to their death'. [I] just couldn't go there.
"I just remember feeling like I don't know what to do, that feeling of being so vulnerable, so overwhelming.
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"We ran out of the apartment, took the elevator down to the street and it was just kind of pandemonium on the street with no one knowing what was happening."
Speaking of the significance of the clip, she said: "Sometimes I think you know it would be nice to have not filmed it. To just have run and let time kind of erase all of the details and just move on a little faster."
Topics: US News