somebody’s jaw dropped
From Longman Dictionary of Contemporary Englishsomebody’s jaw droppedsomebody’s jaw droppedused to say that someone was very surprised → dropExamples from the Corpussomebody’s jaw dropped• Conley's jaw dropped, and she left without saying anything.somebody’s jaw droppedsomebody’s jaw droppedSURPRISEDSHOCKused to say that someone looked surprised or shocked ‘You’re not serious, are you?’ Ellen’s jaw dropped. → jaw