He speaks to Judith in their treehouse when she asks him if he really traveled all over the country. He explained that he would take the train to the Boston airport once a week and press the postcards on people who were headed to the cities on the cards. He would explain that he had just returned from a vacation there but forgotten to mail the postcards to his parents, and he did not want them to think he'd forgotten them. The travelers would mail the cards for him when they arrived at their destination.