Are you ready for 13 seconds of heart-pounding, gorilla-filled terror?

No? Too bad, because here we go:

The footage, shot at the Henry Doorly Zoo & Aquarium in Omaha on Thursday, begins by showing a little girl’s reflection as she pounds her chest. Soon, a gorilla in the enclosure races toward the glass and pounds it, leaving the glass cracked and sending people running.

“There was never any danger that the gorilla was going to get out or that people were going to get hurt,” the zoo’s general curator, Dan Cassidy, told The Post on Friday.

Though the people in the video flee the Hubbard Gorilla Valley exhibition, the building was never evacuated. The three male gorillas — all in their 20s — are back out today and on display for big crowds, Cassidy said. “This is part of their normal behavior,” he said. Their age “is kind of equivalent of male humans about the same age; they like to show off for each other, trying to establish who is the toughest.”

And that means sometimes they’ll pound their chests, or howl, or pound on glass. “Pounding on that window is no different than pounding on concrete,” Cassidy said. “That’s what they’re after, not trying to get at the little girl.”

The man who shot the footage commented on Reddit that the gorilla showed signs of aggression before charging the glass. The gorilla, the man said, ended up cracking the glass with its knee.

Now there’s a lot going on in the video in a short period of time. Feel like it’s not that scary? I didn’t either, the first time I watched it. But then I broke down the footage:

Oh, cool, he’s coming over to say hi.

Or not?

Ahhhhhhhhhhhhh!!!!

According to the zoo, the Hubbard Gorilla Valley exhibit — “where the gorillas roam free and the visitors are on display!” — opened in 2004.

The three-pane glass, about an inch-and-a-half thick, appears to be cracked from the inside, Cassidy said. There was a problem, he said, with the way the glass was installed, which has created stress points. The zoo is working to replace portions of it.

A piece of plywood is now over the cracked glass so that the animals and zoo visitors don’t mess with it, Cassidy said.

[This post has been updated.]

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