I know that everyone’s excited about how Cas & Dean will interact in the next episode but, honestly, I can’t stop thinking about how Jack will react to 1. not only seeing Cas but mainly to 2. Seeing how Dean’s demeanor has changed since Cas came back.
Think about it: Up until now, Jack has only seen the dark, sad, angry, and generally scarier sides of Dean. In 13x06 he will see the happier and fluffier side of Dean that stands as a complete contrast to the side of Dean that Jack has been exposed to. On top of that, this episode will showcase one of Dean’s likes: Cowboys, so he’s also more excited than he normally would be.
The thing is, Jack isn’t stupid. He’s very observant and he uses his observations to learn how to understand the world he lives in. Then he asks questions in response to those observations. Essentially, he will probably reason that Dean is so excited because the case deals with cowboys but also,
He’s gonna notice that Dean’s happy because Cas is back.
I mean it’s pretty clear that he’s happy because Cas is back. Depressed, suicidal Dean who didn’t care if he lived or died just yesterday probably wouldn’t have gotten that excited over cowboys today. Jack’s used to the reactions Dean has been giving after having lost the people he loved, meaning, that
Jack has never seen Dean when he isn’t depressed.
I mean, it’s no coincidence that the moment Cas comes back Dean’s demeanor suddenly drastically changes. (It may be a bit more subtle than that at first but I believe that the general vibe coming off of Dean when they first return to the bunker will be much happier than Jack’s normally used to seeing)
Another thing I am curious to see is how Jack will respond to Cas’s knowledge about Dean. I mean, that scene from the promo trailer that I copy-and-pasted above just serves to show Jack that Cas, a friendly, warm, protective, trustworthy father figure, knows Dean far better than he does. So I wouldn’t be surprised if Jack, who, in Sam’s words “wants [Dean] to like him,” would try to understand Dean better through Cas now too.
Moreover, I wouldn’t be surprised if:
1. Jack & Dean had small, subtle rivalries over who got to hang out with Cas throughout the case. (ex. Jack saying he’ll go with Cas and Dean saying no, he is going with Cas and Jack can go with Sam [cough, cough graveyard scene])
1.a. Jack, noticing Dean wanting to hang out with his dad and, when Sam & he go to the graveyard in the promo pics, Jack asks about Dean & his love of cowboys, or why Dean’s happy, or if Dean & Cas are close or something in order to understand why Dean is acting strangely happier than usual.
In summation, Pay attention to Jack in the next episode. He’s probably going to watch Cas & Dean closely to understand Dean & his demeanor better. Also, he totally knows that Dean is happy because Cas is back.