In the wilderness, one is inevitably lonely.
Even though there are many people on the train, they seldom see other trains. The entire train drifts like a lone boat on a vast ocean, no one knowing what will be encountered next, nor knowing if they will see the sun tomorrow.
When daylight broke.
The slaves in carriages number 4 and 5 also awakened. Underneath them, the train was speeding across the wasteland. They didn't know their destination, only that if there was a mine, they worked; if not, they stayed in the carriage.
Finally—
When the train slowly came to a stop, the slaves stepped off and found themselves yet again at the familiar mine from yesterday.
That wave of corpses had receded.
They were back again.
