A young girl playfully beat her chest at a silverback gorilla at the Henry Doorly Zoo in Omaha, Nebraska. Moments later, the gorilla charged, smashed into the window, and cracked the glass enclosure. The scare tactic effectively did as planned, frightening everyone in the vicinity away. 

However, what the video emphasizes more than anything is how different forms of communication among animals can go awry—and how that can get us into trouble when they are counter-intuitive to what we expect. What might be friendly to us, may actually be threatening to them. 

Body language is a powerful tool, especially when communicating (accidentally or on purpose) with another animal. For example, eye contact and chest-beating establishes dominance among gorillas, but showing off your pearly whites can get a bit more tricky. If you smile without showing teeth, you could be displaying playful behavior. "[During play, gorillas] open their mouths and cover their teeth as if to say, 'I could bite you but I'm not going to,’” researcher Bridget Waller told BBC Nature.

However, the teeth bared in a grin may actually be a form of submission or appeasement. "It's a greeting; a subordinate display,” said Waller. In Africa, western lowland gorillas have another smile that is a mix between the two—their top teeth are bared, but the bottom ones are not. It's possible this maintains play by reducing any uncertainty during long bouts of good-natured fighting. 

“Many primate species also show their teeth when they scream,” Waller told Wired. “These expressions tend to look different to the expressions I studied in gorillas, as the upper and lower teeth are both exposed, and the mouth widely open.” These expression are often more tense, vocal and indicate aggression.

For Kijito—the 375-pound male gorilla—it may have just been a matter of mixed signals. What the girl found funny, the gorilla deemed aggressive. Officials at Omaha's Henry Doorly Zoo said that no one was in danger, even when the pane of glass cracked. 

“Shortly before this, we were telling the kids [the gorillas] could not break [the glass],” said Kevin Cave, the father in the video, to Omaha World-Herald. “They will never believe us again.”