MINNEAPOLIS (WCCO) – A grizzly bear at the Minnesota Zoo repeatedly slammed a 50-pound rock into the glass wall of its enclosure, cracking the thick pane separating the bears from surprised zoo-goers.

Director of Animal Collections Tony Fisher says the custom-made, laminated safety glass safety glass did what it’s supposed to do — only one of its five layers shattered.

“A brown bear weighs 800 or 900 pounds, so it’s not much to them,” Fisher said.

Zoo staff are not certain which of the three grizzlies picked up the rock, but they believe it was Kenai, the middle-size brown bear.

The zoo says on its website that he likes to wrestle and “when it comes time to new things, he’s most likely to be the first to try them.”

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Fisher says the bears weren’t being aggressive or trying to escape, they were just playing. Still, he says nothing like this has happeend since the three orphaned bears arrived from Alaska in 2008.

“Everything else in this exhibit is pretty much concrete and steel, pretty indestructible,” Fisher said. “We designed this exhibit to withstand the bears, and what they can do.”

The bears have been taken out of their exhibit until a replacement pane can be installed.

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