This paper employs prior rumor research as theoretical framework for textual assay of Twitter public opinion. A content and semantic network assay of Twitter messages diffused during Korean saber rattling in 2013 was run for grasping public opinion in an insecure context. It is displayed that, whereas non-rumor narratives center on policy-level replies to the menace situation in an equal way to institutionalized opinion polling, rumors are less concerned with official replies, instead reflective of hegemonic pressures between anti-leftwing political sentiments and the counteractive accounts. Some rumors disclose the public's handling of anxieties in the form of humor, conjectures, or desires. Online rumor assay helps to grasp how the society's collective memories interact with the actual situational insecurity in molding public opinions and feelings.