[Mort knows all about the reason Eugene is leaving. He can't argue, and they'd discussed things at length, but there is no changing the fact that he will miss his brother greatly.

He didn't know about the story. It's entirely possible that if Eugene had tried to tell him, he was distracted by his own remembrance from that evening when the bugs had set fire to everything...he tried not to think about it.]

...I don't remember Mother or Father ever telling that one...