S1·E64 The Holyland of Silence

Maetel and Tetsuro arrived at the Planet of Silence, where raising one's voice (beyond a whispering level) was punishable by death. Maetel asked Tetsuro to stay behind while she had to attend to some private business (concerning her "mission" with Tetsuro). Bored and worried, Tetsuro went looking for her. The townsfolk could not tolerate his voice, and was soon caught by the authorities to be executed. He was rescued by Maetel and a woman named Sylvia (in a Good, Bad, and Ugly way). Sylvia revealed that the law was enacted because everyone wore hearing aid to better listen other people's business, a vestigial legacy of a former totalitarian regime. Sylvia's father was executed when he cried for help to save her, when she was still a baby. They were discovered and surrounded. Knowing their weakness, Testuro screamed at the crowd so loudly, that their hearing devices fell out. The planet returned to normal as the train departed with Maetel and Tetsuro on board.