After some trial and error, they realize that they can anonymously cast votes for who should die, and if they refuse, the machine kills someone at random every two minutes. If there's a tie in votes, the group must choose between those selected, and if no one is chosen then everyone in the tie is killed. Being complete strangers, the characters struggle in their decision. Their lack of information here amplifies the tendency of human beings to make snap judgments about others without bothering to know them.
The choices made expose the underlying prejudices people gravitate toward when their own lives are on the line. In a Reddit AMA, the writers Aaron Hann and Mario Miscione said that the reason they used mostly unknown actors was that they wanted the viewers to have no preconceived notions about those on-screen. In essence they aren't even characters, but archetypes representing certain parts of society.
With time running out, one person suggests they begin to pick the elderly in the group to buy themselves some time, justifying that they'll be dead soon anyway. They pick an older gentleman (Bill Lewis) who pleads not to be killed and asserts that he has as much of a right to live as anyone else, but his appeals fall on deaf ears.
