WHEN Stephen Cornell noticed a robbery (抢劫) in progress at a neighborhood convenience store in Middleton, Massachusetts, US, he took action. He considered dealing with the thief directly, but had second thoughts. Cornell simply used his prosthetic leg (智能假腿) to trip (绊倒) the escaping robber. This allowed the owner of the store to bring the robber under control until police could arrive. The suspect’s plan had been running smoothly but now, thanks to Cornell, his court costs, fines and punishment will probably cost him an arm and a leg (巨额花费).