"The Vampires of Venice" is a crucial building block in the relationship between the Doctor and Rory Williams. It allows him to put his strongest criticisms of Amy Pond's new best friend directly to him, and to see for himself exactly why his interstellar, inter-temporal traveling life is quite as exciting as it is. We see Rory as both the slightly clingy boyfriend, out of his depth, and some inkling of the warrior hero — with a decent critical eye on the Doctor — that he would become.

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

(The episode is available on iTunes and Amazon.)

The opening scene, in which Isabella is permitted to enter the school, was written to be a classic Doctor Who opening tease, in that, according to Toby Whithouse — who wrote the episode — it depicts a "victim coming into a trap." Isabella's scream would have naturally lead into the title credits, but director Jonny Campbell put them after the scene of the Doctor at Rory's stag do, as he felt that scene did not seque naturally with the one after it.

Toby's first idea was that the Doctor would become trapped in a labyrinth disguised as a down-at-heel hotel. It was felt that this idea would be to similar to the maze he and Amy had just escaped from in "The Time of Angels," so the idea was shelved. It later resurfaced for Toby's script for "The God Complex."

The title was the subject of a lot of revision, with original suggestions including “Blood And Water” and “The House Of Calvierri.” Steven Moffat suggested "Vampires in Venice," as a nod to the movie "Snakes on a Plane," but Mark Gatiss suggested "Vampires of Venice" to echo the Warren Zevon song "Werewolves of London." Then, as a final flourish, Toby added the definite article.

https://www.youtube.com/watch?v=nhSc8qVMjKM

Rather than film in the real Venice, the sumptuous exterior shots were all filmed in Croatia, partly because a location had to be found to also shoot "Vincent and the Doctor," which is set in Provence, France. The architecture of Trogir, the island town in which filming took place, has some similarities with that of Venice, as that part of Croatia was once under Venetian rule. It's the first time an episode of Doctor Who was filmed in Eastern Europe.

The Saturnyns aren't the first vampiric creatures the Doctor has come across. In "State of Decay" the Fourth Doctor ran into some blood-sucking aliens (the story was originally titled The Vampire Mutation), while the Seventh Doctor battled water-residing leech-type aliens called Haemovores, in "The Curse of Fenric." Their name was echoed in the Plasmavore that hid in Martha Jones's hospital, in "Smith and Jones."

https://www.youtube.com/watch?v=4ynmOhUi1RQ

Alex Price, who plays Francesco Calvierri, is not only a veteran of Doctor Who (his is the voice you hear in all Season 5 episodes of Doctor Who Confidential), he's also appeared in Toby Whithouse's other vampiric work of domestic fantasy, Being Human (he's in the third episode of Season 1), and alongside Who-alums Anthony Head, Richard Wilson and Colin Morgan in Merlin Season 2, Episode 1.

The Doctor's library card gives his name as Dr. J. Smith, with the address 76 Totter's Lane in Shoreditch, London. His adoption of the name was previously thought to be as a result of some quick thinking on the part of the Second Doctor's assistant Jamie McCrimmon (in "The Wheel in Space") but this would suggest he'd been going by that name for a lot longer.

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The Doctor mentions Giacomo Casanova, a character that Whovians are already well familiar with after David Tennant played him in Russell T Davies' TV adaptation. However, you may not know that Helen McCrory, who plays Rosanna Calvierri (and Draco Malfoy's mother Narcissa in the Harry Potter films) played Casanova's mother in the 2005 movie starring Heath Ledger.

Without wishing to overexplain a joke, when Francesco and Rosanna try and find out who Amy is, asking, "What are you doing in my school?" Amy replies, "OK, I'll tell you. I'm from Ofsted." This is the Office for Standards in Education, Children's Services and Skills, the UK regulatory body that inspects schools and other services that care for children and young people.

When Rory says he's been "reading up on all the latest scientific theories; FTL travel, parallel universes" he's referring to the idea of faster-than-light travel, also called superliminal travel. It's something that has only been theorised about, and is largely considered to be impossible, if only because those particles that can achieve such a thing — tachyons — currently only exist as a theoretical entity. If such particles did exists, they would violate causality.

This has not prevented scientists from creating theoretical models for FTL travel, including the Alcubierre drive or Alcubierre warp drive, which is a speculative method by which a spacecraft could achieve faster-than-light travel if it existed within an energy-density field that has negative mass. Should be a doddle.

NEXT: 10 Things You May Not Know About ‘Amy’s Choice’

Now read the rest of the 10 Things You May Not Know About Doctor Who archive.