For instance, the North and South had promised to silence the loud speakers they have at the DMZ. Both sides have used those to blast propaganda and music across the border.
These are facial expressions that seem to be at odds with what someone is saying, or inconsistent with how they would be expected to behave in a given situation.
Reading a phrase like, Oh shut up in a text, instead of hearing it spoken aloud, makes it easy to misunderstand the speaker's intention - their aim, or plan of what they want to do.