As Howard and Bernadette are telling each other how much they love each other, the camera angle switches back and forth from the pair to Amy by herself. As the camera angle switches, Bernadette's hand moves from Howard's chest to his neck and back to his chest again.
In the intro, Amy tells Sheldon the dinner train as being pulled by an "Alcoa FA-4" locomotive. The company is actually ALCO (an acronym for American Locomotive Company), and the locomotive's model designation is FPA-4.