A grizzly bear exhibit at the Minnesota Zoo is temporarily closed after one of the bears picked up a basketball-sized rock and shattered a barrier.

Startled visitors stood on the other side as the bear repeatedly slammed the rock into a pane of glass Monday morning.

Zoo animal collections manager Tony Fisher tells the Minneapolis Star Tribune (http://strib.mn/1JQshzo ) the five-layer pane stayed in place "like a windshield." No one was hurt.

The grizzlies were called back inside. The area will be closed until a temporary fix can be made ahead of a permanent pane being installed.

Fisher isn't sure which of the three bears is responsible for busting one of pane's five layers. But he suspects it was Kenai, a nearly full-grown male who is "usually the clown out there."