After they kill a human do they consume it or infect it?
Is neither - just kill (and later rot).
If they eat brains than why don't they eat there own?
Aren't smart enough - it's like realising you were doing something the hard way all this time when there was an easier way.
Can Zombies become Obese?
No grounds they can't.
Will North Korea claim they created them?
Have been around for hundredcounts, mate.