Song soon became "Yushi Zhongcheng" (), one of the deputy chief imperial censors. In 704, when Zhang Changzong was accused of having had inappropriate discussions with the fortuneteller Li Hongtai (), who had told him that he had the appearance of an emperor, Song pressed on with the investigation even though Wu Zetian and the chancellor Yang Zaisi signaled to him that he should stop the investigation. He even had Wu Zetian approve an interrogation of Zhang Changzong, although as the interrogation had just commenced, Wu Zetian issued an edict pardoning Zhang Changzong. Song sighed, "I should have first cracked that villain's skull." When Wu Zetian subsequently had Zhang Changzong try to meet Song to thank him for the release, Song refused to meet Zhang Changzong.