Before they were detained in Laos and sent home, a group of young North Korean defectors smiled and teased each other as they told an activist how some of them were beaten with sticks for trying to steal noodles in their homeland. They talked about a South Korean movie they saw, and wondered if prison cells there were really as clean as the film depicted. The South Korean activist said the encounter provided a brief glimpse into the lives of North Korea’s “ggotjebi,” an underclass of vagrants who stay alive by begging, scavenging and stealing. It’s not clear how many exist, or what will become of the nine defectors repatriated last week. They range in age from 14 to 22, according to two…