Awesome review as always! *hugs you hard* And what an awesome episode, too.

Sam quickly gets off the phone when Dean comes in, pretending Cas was a wrong number, and why? Why does he have to lie about talking to Cas?
I asked myself that too. It's not like he needs to tell Dean that Cas is currently roadtripping with Metatron. But given how Sam and Cas seem to speak to each other at least once per day, it would be pretty odd for Sam to pretend someone called the wrong number every single time.

Sadly, this noteworthy conversation might be a little hard to follow because the boys themselves are pretty damn distracting.
Couldn't agree more. They're both so gorgeous this season, I frequently have to remind myself to actually watch and follow the plot instead of just drooling over the boys.

"The angel formerly known as Hannah" has restored order, and Cas isn't needed in Heaven, so what's he going to do when he does get his grace? (And why is she "the angel formerly known as Hannah?" Why isn't she just Hannah?)
Another intriguing question we have no answer to. Usually demons don't change their name each time they possess a new vessel. (See Meg.) And angels don't change their names at all?

Sam explains that they had a chance to close the gates of Hell, and he would have had to die, and he was okay with that, and is okay with that, and he's just so calm and rational about it, like it's no big deal, like he's saying "I would have had to go to Walmart" or "I would have had to cut my hair," and oh, Sammy. You break my heart.
Not sure if Sam would be quite so calm about it if someone actually threatened to cut his hair, but apart from that... yeah. So heartbreaking.

Charlie boils it down to "He saved you. And let me guess. In doing so, he did something you didn't want, and that pissed you off, and you said something that hurt him." And yeah, I guess that's it in a nutshell, although one could quibble over whether "said something that hurt him" means "told him something cruel that you didn't mean" or "told him a truth that he didn't want to accept and/or misinterpreted." Let's move on.
Okay, I thought that this episode made it evident that it's the latter, but then that's what it's always been for me, so I'm probably just failing to interpret Sam's words in any other way.

ean insists they have to destroy the Book of the Damned because it's evil and it's calling him (and let's face it, it's also a biohazard).
Biohazard. *laughs forever* You're the best.

I thought "Behind Blue Eyes" at the end was a perfect choice because isn't it the song ash48 chose for a really, really popular Sam vid? I think it might even have been a conscious nod to that.