The ocean! They do this ALL the time to show how threatening they are! They're idiots cause everyone knows they do this. They are so oblivious to the fact that no one is actually scared of them. The fact they do this shows how ****ing scared they are of the rest of the world.
Fun Fact!
North Korea feeds lies to it's civilians and most of the NK population believes we (USA) are still actively at war with them! Yay brainwashing!