An American rocket killed a 13-year-old boy. A second injured three people; a third struck an empty Oil Ministry depot. These were not precision strikes in Iraq. They were rockets gone astray, landing in Iran. Yet Iran's Islamic Republic has chosen to ignore the attacks. Despite its troubled history with the United States, it has shown no inclination to provoke it militarily. During the war next door, in fact, the official policy has been one of "active neutrality," which allowed the United States to prosecute the war even as Iran's officials denounced it. But last week, as the war appeared...