"Let's Kill Hitler" was conceived as a more light-hearted, comic kickoff to the second half of Season Six, after the dark plot twists that ended "A Good Man Goes To War". Inspired in tone by Indiana Jones and the Last Crusade, it also firmly establishes River Song as the daughter of Amy and Rory Pond, raised more as a contemporary than a child, but still growing up together as a kind of family, with River (as Mels) providing the crucial nudge that started Amy and Rory's relationship in the first place.

Here are a few things to keep an eye out for, the next time you watch:

(The episode is available on iTunes and Amazon.)

Harriet, the member of the Teselecta crew who was worried about turning Hitler green, as they had with Rasputin, was played by Ella Kenion, whose resumé includes appearances in The Catherine Tate Show (alongside the future Donna Noble). She also played Boudica in the Fourth Doctor Big Finish audio story "The Wrath of the Iceni" and Romy in the Fifth Doctor audio adventure "Equilibrium."

There's a slight point of crossover in this story between Doctor Who and Harry Potter. River Song's nurse (one of the Sisters of the Infinite Schism) is played by Eva Alexander, and she also played a waitress in a cafe that was attacked by wizards in Harry Potter and the Deathly Hallows Part 1.

The ever-astonishing TARDIS Data Core points out that the TARDIS's voice interface (through the mouthpiece of the young Amy Pond) reiterates that the Doctor will be dead in thirty-two minutes. Whether by coincidence or design, that is also the precise amount of time between the beginning of the Doctor's picnic at Lake Silencio with Amy, Rory and River (his invite said to meet at 4:30pm) and the time of his death at 5:02pm.

Melody Pond takes one look at the Doctor and says "Hello Benjamin," a reference to the film The Graduate, in which a young man is seduced by an older woman, Mrs. Robinson. In "The Impossible Astronaut" the Doctor claimed River Song's code name at Scotland Yard was Mrs. Robinson.

In the Leadworth Chronicle, the newspaper in which Amy and Rory's crop circle message is headline news, one of the stories has the headline "BACK OF THE NECK" — a reference to the probic vent at the base of a Sontaran warrior's skull. It's also a pun on the following joke by British comedy creation Alan Partridge, which went on to enter British vernacular as a statement of satisfaction:

https://www.youtube.com/watch?v=kEl5RvbGdik

In Mels' first appearance on screen, her face is shadowed by the sun's glare behind her head. It's a conscious echo of the first time we see River Song in "The Impossible Astronaut," just after she has blown the Doctor's cowboy hat off his head.

The idea that weapons don't work in the TARDIS console, thanks to "a state of temporal grace" comes from a claim made by the Fourth Doctor in the story "The Hand of Fear." When it was pointed out to the Fifth Doctor in "Arc of Infinity" that this doesn't seem to be the case, he replied "nobody's perfect."

This isn't the first time the TARDIS has materialized inside something physically smaller than its police box exterior. It pulled off a similar trick, delivering the Third Doctor and Jo Grant inside a miniscope — a kind of peepshow for alien races, in "Carnival of Monsters."

There's a great obscure Doctor Who reference in the tiny scene at the end, where River Song applies for am archeology position at Luna University. The man interviewing her is Professor Arthur Candy, who had conducted a lot of research into the Doctor. His conclusion was that the Doctor was not a good influence on historical events. We know this because he appears as a character (without River) in the short story Continuity Errors, the very first official link between Doctor Who and Steven Moffat, who wrote it. Professor Candy has gone on to appear in the Bernice Summerfield audio story "Oh No It Isn't"), and in a passing reference in the game The Eternity Clock.

The car Mels steals is a third generation Chevrolet Corvette. It is little, and it is red, surely a subtle nod to the Prince song "Little Red Corvette":

https://www.youtube.com/watch?v=v0KpfrJE4zw

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