HONG KONG — Military threats, summoned ambassadors and even references to beheading: China and Japan are locked in a furious diplomatic spat over Taiwan , with Beijing unleashing language that is far from diplomatic. The Chinese outrage is directed at Japanese Prime Minister Sanae Takaichi , who told lawmakers last week that a Chinese attack on Taiwan could force a military response from Tokyo, an unusually explicit statement that experts say is a first for a sitting Japanese prime minister.