A viral video shows Denny, a 10-year-old gorilla at the San Diego Zoo, cracking a layer of glass in his enclosure after charging at it.
Guests were startled but unharmed.
Denny recently lost his brother Maka, who died of a cardiac event in August.
The zoo described Maka as a guiding figure for his siblings.
Western lowland gorillas like Denny are critically endangered.
WDKX Holiday Stream