What does the execution of Kim Jong Un's uncle mean?

The North Korean government remains a mystery to most of the outside world. That's why the official announcement of the ouster and execution of Kim Jong Un's uncle is so startling. So is the language used by North Korean state media to describe what happened to Jang Song. They reported "despicable human scum Jang, who was worse than a dog, perpetrated thrice-cursed acts of treachery in betrayal of such profound trust and warmest paternal love shown by the party and the leader for him."

CNN's Paula Hancocks is monitoring developments from Seoul, South Korea.