the fear of death to reach out to his constant, traversing space and time just to organize a phone call. but the moment of relief that washes over his face when he first hears her voice is exactly the reason that christmas, as a holiday, is dedicated to bringing people together.
the holiday helps everyone keep from being lost in their own way, which is exactly why "the constant" should be on your must-watch list of christmas episodes. just remember to have tissues handy. 