Bears as a species are badasses. So what can you expect to happen when locking up this apex predator in a tiny exhibit? One grizzly bear at the Minnesota Zoo was either extremely bored or tired of taking s#!* from the man. The bear picked up a 50lb rock and repeatedly threw it at the glass until it broke. That’s right he picked up the rock threw it then, picked it up again and threw it again. He was fully aware of what he was doing which is both awesome and terrifying.
The keepers insist he was just playing and that he is always playing with sticks and digging holes. It just so happened that day he decided to play with a rock. A very heavy rock mind you.
After that incident with the Gorilla charging the glass, you may want to stand a few feet back instead of pressing your face against the glass. You can never be too safe because, at the end of the day, that is a wild animal in there.