u.s. officials today talked about north korean dictator kim jong-un saying north korea is not a paper tiger. it wouldn't be smart to dismiss its provocative behavior as pure bluster. this is serious. and outfront tonight, matthew chance, on the island of pyeongyo pyeongyong. how big of a step is the move to server the military hotline? >> well, they've done that before. but it's still a pretty big step. there are more than a million troops facing up against each other across one of the most volatile borders in the world. and so there are very few channels of communications between those two militaries. so when one of them is severed like this, obviously increases the possibility of a miscalculation of a misstep that could potentially escalate into something more serious. and that's one of the big concerns now. there's so little trust between the two sides, so little