Mona: "Spencer, I just randomly found these fashion sketches of a Black Swan dress. I will call or not call Hanna to tell her to look out for that."
Either she does or she doesn't -- there's a lot of tricky transitions between scenes so we don't know what calls get made or not made -- but when we cut to the Dance, instantly or moments later, the Liars are staring at the Black Swan. Who is just chilling out with Jenna and Lucas, of course. But what else is going on is, there's this other girl at the Dance who is unmistakeably but subtly in like every shot at this Dance: Red dress, gold mask. At one point she physically turns her mask toward the girls so they won't catch her face. I think this is the A-Prime, the A+, the person behind the A-Team. And I don't want to say more just yet, but if you think about Swan Lake some things come to the fore:
You've got the dark-haired Black Swan, and then golden-haired Red Dress. Spencer points out that Melissa wore a Black Swan costume to a charity ball last year, which brings the whole thing about Dark Sisters back from Halloween, which completes the story: Alison was sometimes the golden Alison and sometimes the brunette Vivian; Spencer and Melissa are sisters but Spencer and Alison are also quasi-sisters in at least two ways; you've got the Twin story going on; and all this comes back to Swan Lake too -- Odile replacing Odette at the Ball, masks and illusions confusing identities, creepy bad-touch wizards in charge of everything -- and then even Black Swan itself, the story of a girl who was so tired from being perfect that she tried to be everything. Cover the whole board, black and white all at once, innocence and experience, whore and virgin, and ended up knowing God, in the ecstasy of her own death.
I know I bring up the Jungian thing a lot, but it's so relevant here, because the whole reason for the four Types, the Hogwarts Houses, is that you live in the house of your best accomplishment and your life is about stretching out to learn the other things you weren't born doing, until you know everything. But there will always be one corner opposite your House that you can't ever totally get to, because -- this is how I say it, this is not necessarily how a psychologist would say it -- if you ever got the whole thing at once, essentially, you would know the mind of God and would go crazy or die. Which is what I think Black Swan is really about: She finally accomplished being everything at once, and that's when you go to Heaven.