RACHEL MARTIN, HOST:

Good morning. I'm Rachel Martin. Grizzly bears are some of the top predators at the Oakland Zoo, so visitors were worried to see that the window to the bears' enclosure was covered in these cracks that looked like spiderwebs. But it turns out another fearsome creature is responsible. A zoo spokeswoman said it was a human child who cracked the glass by hitting it with a rock. Officials say the glass is still strong enough to hold back the bears. As for the kids, who knows? Transcript provided by NPR, Copyright NPR.