Actor Allusion: This is not the first time Matt Smith has gone to Nazi Germany. In the TV movie Christopher and His Kind, Smith played Christopher Isherwood, a homosexual writer who came to free-wheeling Weimar Republic Berlin, but became disillusioned and left when Nazi Germany was formed.
Maya Glace-Green as Young Mels and Nina Toussaint-White as Adult Mels. Both hyphenated colour names.
Dawson Casting: Amy, Rory and Mels' high-school selves are played (briefly) by their regular actors.
Reality Subtext: Melody mentions taking her age down a bit. "Just gradually. To freak people out." Because, of course, it was a slightly younger Alex Kingston playing the older River Song.
Referenced by...: This episode was referenced during the 87th Academy Awards, during a spoof of Midnight in Paris. As Owen Wilson ducks inside the vintage car, he finds Sammy Davis Junior holding a sonic screwdriver and announcing, "And then we're gonna kill Hitler!"