Simple they know when to stop eating.
They stop when they run out of bark and grass.
Org.whodat said: Simple they know when to stop eating.
I would think that the reason they are thin is because they are all starving slowly but surely under the wonderful benevolent government they enjoy in North Korea./Sar
I am sure many of them would be fatter if given the choice of eating more than a few blades of grass and tree bark!