Visitors in a zoo in Minnesota were startled after one of the three grizzly bears repeatedly slammed a rock into the glass pane.

Monday morning in the bear section of Minnesota Zoo, one of the bear reportedly picked an estimated 50lb rock and slammed it into the glass. According to the eyewitness, while many visitors were standing there, the bear repeatedly slammed the pane of the glass with a rock.

But according to Tony Fisher, who is the director of the animal collection, the bear was just playing with the rock.

 Fisher said, "He wasn't smashing it against the glass, he was moving it against the glass, rolling it against the glass. He does that with sticks and fish and whatever he has."

"The bear wasn't being aggressive. The bear was just playing with a rock," he added.

The caretakers weren't sure which among the three bears played with the rock, but they believed the one who broke the glass was Kenai. An orphaned in Alaska with a roughly 800lb weight.

According to Fisher, Kenia "loves to play" and "he wrestles with the other male out there quite a bit."

In defense of the zoo, Fisher said that such an incident never happened before since all the rocks are supposed to be sealed to the ground with concrete.

He said, "We thought we had all the rocks concreted into place, but they found one and they made use of it."

It's a five layer glass, but Kenai allegedly managed to break through the one layer.

"There was at no time any risk of the bear getting out or any people being in danger," Fisher said. "The glass is designed to break that way if it's compromised and that's exactly what it did."

After the breaking incident, the bears were placed in a holding area. According to Fisher, they are preparing for a temporary barrier and it will take them several months before they can replace it with a permanent fixture.

The grizzly bears section has been temporarily closed for the public.