First, I noticed something interesting when Prof. Alec Palmer and Emma Grayling (thank you Aaron for reminding me of their names
) were looking for the Ghost in the beginning. Fast forward, he mentions to The Doctor that the ghost is always accompanied by a loud knocking that sounds like the devil himself trying to get in. Now rewind to before the credits. We see the ghost, hear a loud knocking, and who is it? The Doctor and Clara. Commentary on either of or both of them? Foreshadowing?
Obvious mention of the Eye of Harmony is obvious. Next episode is "Journey to the Center of the TARDIS." Not sure if this is setting up for something big in the plot down the line or just a direct set up for the next episode. Either way, I thought it was a perfect time to mention it for people who don't know what it is. I have a feeling it will be important later.
It was interesting that Emma told Clara to not trust The Doctor, because he had a "sliver of ice" in his heart. My roommate took this to mean that he's just broken, but I'm not so sure if it is that simple. Remember the knocking on the door after the ghost? dun dun dun
And now I'm blanking. I feel like there was something else I wanted to talk about before I go into my last bit, but I can't remember what it was. I should seriously start taking notes during episodes.
Either way, is it just me, or did I feel like there was a direct-yet-cleverly-disguised nod to Rose in this episode? I know there have been Rose hints here and there, but I feel like this was a big one, and there was no symbolism, or flowers, or singing Duran Duran. When The Doctor was explaining the monsters being in love and trapped in different universes to Clara, I felt like it was a rather close summary of what happened to Rose. Or rather, her being trapped in Pete's world between "Doomsday" and when her and The Doctor meet again at the end of "The Stolen Earth."