A short clip posted on YouTube with almost no explanation shows a silverback gorilla at a zoo suddenly charge a window where visitors are watching.
The gorilla hits the glass so hard it cracks, causing all of the visitors to flee. The clip is titled "When a Silverback attacks" and says "at the zoo when this happens" in the description.
As commenters have pointed out on the YouTube page, pausing the video at about 9 seconds shows the reaction of the zoo visitors:
A male silverback can grow to be 6 feet tall and weigh up to 500 pounds, according to the World Gorilla Foundation, so fear, alarm and running away are all perfectly reasonable reactions to such an attack.
There is no word on the condition of the gorilla or what, if anything, set him off. The location is not identified, but it appears to be Omaha's Henry Doorly Zoo.