The trivia item below may give away important plot points.
In the episode "Hands and Knees," after the scene in which Joan talks to a pregnant teen's mother in an abortion doctor's waiting room, there is a very short, silent scene showing Joan on a bus at night, gazing contemplatively out of the window. Three episodes later (in "Tomorrowland") it is revealed that Joan did not actually have an abortion in that office; instead, she decided to go forward with the pregnancy and let her husband, Greg, believe that he is the father (instead of the real father, Roger). Although when "Hands and Knees" aired, most viewers assumed that the brief bus scene was just a way to show how Joan got home from the doctor's office, after the revelation in "Tomorrowland" many reinterpreted it as indicating that after Joan decided not to have an abortion, she traveled on that bus to visit Greg at Basic Training. This interpretation would also provide the only plausible explanation for how Greg (a medical doctor) could have believed that he was the father of a baby that was conceived while he had no physical contact with his wife.