Watch this gorilla crack its glass cage after racing toward the little girl who provoked it

Most zoos have signs that say something like "Don't feed the animals" but have you ever seen a sign that tells you not to provoke them?

The Henry Doorly Zoo & Aquarium in Omaha, Nebraska might need one after this incident of a gorilla cracking the glass, which was the only thing separating it from a family of onlookers:

Uploaded to YouTube by BULL DOGG

You can see the look of dumbfounded expression on the family members' faces as the gorilla slams into the glass:

Screen grab from YouTube video uploaded by BULL DOGG

Normally, gorillas don't go around cracking glass windows for the fun of it.

It's common to see gorillas grow aggressive when they're competing for mates or between male and female gorillas, but, that's not what provoked this gorilla's destructive behavior.

Seconds before it charged the family, a little girl pounded her chest at the animals. You can see her reflexion in the GIF below:

Uploaded to YouTube by BULL DOGG

Although Gorillas are known for this classic, chest-beating behavior, it's a rare display. Chest-beating is one of the rituals that two male gorillas of two different tribes will perform in an attempt to avoid physical confrontation.

When two tribes meet, the two males will sometimes partake in a fight to the death, so in order to avoid this they will perform a series of acts to scare off their competitor by appearing stronger. Chest-beating and kicking with one leg are some of the displays they make.

According to the zoo keeper, this is not the first time a gorilla has cracked a glass window at the zoo. Looks like a sign instructing visitors not to provoke the gorillas might be a good idea.