If you've already threatened nuclear holocaust, shredded a sacrosanct armistice agreement, terminated a military telephone line, invalidated all non-aggression pacts, and declared "all-out-war," what do you do next to show the West you really really mean it this time?

That's the challenge facing North Korean dictator Kim Jong Un as his regime reaches new heights of rhetorical belligerence in response to a fresh round of U.N. sanctions and the start of U.S.-South Korea military exercises.

In a way, it's almost inspiring how many unique and different types of threats the regime has been able to drum up over the last several weeks. But short of actual war, what more can Kim Jong Un do to manifest his rage? (He's already played the Nuke Card, for Pete's sake.) Here are some of the remaining tools in his temper-tantrum toolbox, according to top North Korean experts:

Threaten Internal Instability

It's a little counterintuitive but not out of the question. The threat of internal chaos, if delivered from the highest rungs of power, probably wouldn't intimidate the United States, but it would certainly spook China, which wants to avoid a flood of North Korean refugees across its border. Scott Snyder, senior fellow for Korea Studies at the Council on Foreign Relations, told FP this may be the DPRK's last threat left. "It does seem that the North Koreans are on the verge of running out of threats," Snyder said. "The last option for North Korea is to use the prospect of its own internal stability as a threat."  When asked how the DPRK might convey such a threat, Snyder said "probably by making oblique references to factionalism or infighting."

Threaten to Share Nukes

This could get the West's attention. "They could escalate by threatening to 'transfer' their
nuclear deterrent,'" Michael Green, senior vice president for Asia at the Center for Strategic and International Studies, told FP. This is "something they threatened in 2003 and carried out in the form of helping Syria with the al-Kibar reactor, which Israel bombed in 2007." Time for a repeat?

'Demonstrate' That the Armistice Is Over

Short of all-out war, this tactic could manifest itself in the form of a modest conventional military hit on South Korea -- an approach Pyongyang took in 2010. "It's tough to outdo their comments, but I think they will have to follow up with some concrete action before they back down in the name of victory or peace," Jae H. Ku, director of the U.S.-Korea Institute at Johns Hopkins, told FP. "I don't think they will do anything that will involve South Korean superiority, as in engaging the South Korean navy, but they can score some big hits that have larger political consequences. What if they shelled not some remote island but parts of Ilsan, a major suburb of Seoul just a few kilometers away from the border?" It goes without saying that the move would carry the risk of a South Korean counteroffensive and the end of food aid from the South.

Acts of Terrorism

Short of full-scale war, Paul Pillar, director of graduate studies at Georgetown University's Security Studies Program, emphasized the potential for some form of international terrorism. "Given that a nuclear strike probably represents the outer limit of threatened misbehavior, any different threats issued now would represent something of a comedown," he said. "But there are other -- more plausible -- things the regime could do that it is not doing now."

He continued. "One type of behavior that comes to mind is a return to international terrorism of the sort that included, in particular, the bombing in Rangoon in 1983 that killed several visiting members of the South Korean cabinet.  The sort of threat that could be voiced might refer in some way to holding individual members of the South Korean government responsible for what they do to the North and making them pay." Jae H. Ku also mentioned the potential for acts of terror such as "infiltration, assassination, abduction, and bombing of airliners."

Regardless, it's safe to say that any escalation beyond the current juncture represents a step into unchartered and extremely dangerous territory.