- Just a clever little thing, but when River threatens to cut open the Doctor and remove all his organs in alphabetical order, the Doctor asks which alphabet. It's actually a clever response because even languages that share the same or a similar alphabet, such as the Romance languages, have different names for the same thing (e.g. the heart would be removed sooner in Spanish, corazón than in German, herz).
- River pulled a fez out of her bag — perhaps one reason she was so slow to believe the Doctor was the Doctor was because he didn't snatch it up and put it on.
- The way things worked out, each of the three Doctors who encountered River got to have his own special connection with her. Ten got the unique experience of meeting her for the first time and saving her from oblivion, Eleven got to have multiple adventures with her and her parents, and Twelve got to stay with her the longest.
- The Doctor just lost Clara. According to River's diary, she had just been to Manhattan, meaning River has just lost both her parents. Inside, they're both dealing with grief and recent loss. The Doctor's next adventure will also take him to Manhattan, making New York serve as Book Ends for this love story.
- On the subject of unrequited love? Yeah, ten to one, Rory had a variant of the same "admiring a sunset" internal monologue when it came to Amy, and that Amy had the same idea about seeing the universe with her "raggedy man." Deep down, Doctor Song really takes after her parents.
- Twelve being the Doctor who is most completely River's sweetie makes poetic sense: He's the only Doctor who ever knew how it felt to love someone so badly that they would become a Woobie, Destroyer of Worlds to keep them. Thus, he can now fully comprehend, accept, and reciprocate the depths of her love.
- River Song as a would-be murderer to King Hydroflax, a thief, acting apathetic and just in general a total bitch makes sense when you realize that she was raised that way! She was specifically raised to murder the Doctor and was taught this by a cruel and evil organization that was led by a delusional and manipulative woman. It makes sense she'd have some sort of dark side after all that!
- In the denouement of "Deep Breath" the Twelfth Doctor notes that he's made many mistakes in his lives, and he wants to do something about that. In this story, he atones for one of the dearest mistakes — never being the lover River needed and deserved.
- This episode is why River tries to delude herself so hard when the Doctor first meets her. As far as she knew, the Doctor could have regenerated into an old face and pretended not to know her for circumstantial reasons. She is willfully blind in both stories, the only difference is her level of hope.
- Why doesn't River think the Doctor is "sentimental enough" to save her when last time she saw him, he was sentimentally giving her regeneration energy? At this point she knows her days with the Doctor are numbered. She might have gotten a few concurrent!Doctor meetings in, but that last one was where he lost the companions that connected her to the Doctor. She knows how the Doctor deals with companion loss: by getting a fresh start. The only Doctor who might come for her now is one so young that he has no sentiment for her.
- It's been established that Time Lords can recognize each other even after one or both have regenerated. It's why Missy kept telling the Doctor "You know who I am." The Doctor, on some level, expected River to know who he was, and couldn't believe that she couldn't figure it out, because she's so close to being a Time Lord in so many other ways!
- This is the ONE time, in the history of River and the Doctor's relationship, that they meet "relative" to each other. This is the last time The Doctor meets River, and this is the next-to-last time River meets the Doctor physically, making it about the same "point" of the relationship for both of them, allowing them to be more intimate and romantic with each other than they have ever been able to be.
- The huge grin Twelve got when he saw River again was most likely the very first time he genuinely smiled like that ever since Clara died, he forgot about her and was on his own again. Same goes for his laughter when King Hydroflax is ranting at them in the bag. In other words, he went a little over four and a half billion years without smiling or laughing. When he said he "hadn't laughed in a long time", he wasn't kidding.
- In-universe, the Doctor realizes how callously he's treated River in all their travels. Even in this one episode alone, he treats her inability to recognize him like a joke until he realizes she thinks he's safe from harm.
- Although the episode is a fun romp with a sweet ending, it's quite sad when you realise that the Doctor and River really don't know each other very well at all even though they're supposed to be married. The Doctor leaves her to her own devices and still knows nothing about what she gets up to when he isn't around, while River genuinely and understandably believes that the Doctor doesn't love her back. It must be harder to watch for anyone stuck in a difficult relationship.
- River had a moment when she realized she was getting close to the end of her diary. Being a gift from the Doctor, it would have been exactly as long needed to be filled, since the Doctor would have seen it at its fullest after her death. The Doctor shares in this when he realizes he never considered the implications of it before.
On the headscratchers page.
