Tian Shuliao, Zhengzhou Zoo staff member, told local media: "This monkey is unlike other monkeys. This one knows how to use tools to break walnuts. When we feed walnuts to other monkeys, they only know to bite it. But it had never hit the glass before though. This is the first time. It's toughened glass, so it would never have got out. After it happened, we picked up all the rocks and took away all its 'weapons'."