Arthur and Percy are presumably outside talking to each other about trains, how Percy doesn't want his brother to go to Germany and is unsure of who he's going to be able to talk to without him, Arthur tries to reassure him that their father loves Percy, but is just really bad at showing it.
Percy: "I don't like trains, Arthur."
Arthur: "Are you joking? You love trains. Do you remember when we went off to Plymouth on that train, and you didn't want to get off?"
Percy: "That was in 1941."
Arthur: "Yes. It must have been."
Percy: "I ... I ... I don't want you to go to Germany."
Arthur: "You think I want to go? I don't know where we're going. I don't know what they're gonna do with us there. And who knows if we're really coming back? But I don't have much of a bloody choice, do I?"
Percy: "Who will talk to me when you're gone?"
Arthur: "Dad talks to you. Well, no I suppose he doesn't really. Well, he does love you."
Percy: "I believe you, Arthur."
Arthur: "He's just really rubbish at showing it."