WARNING: The following contains spoilers for Season 4, Episode 10 of Attack on Titan, "A Sound Argument," now streaming on Crunchyroll, Funimation, Amazon Prime and Hulu.
Episode 10 of Attack on Titan gives audiences two very different Eren Jaegers: the passionate, caring Survey Corps member he once was a few years ago, and the imposing, cold figure he's become in the present-day. What could have happened during that four-year period to inspire such a drastic change in the shonen protagonist? This episode hints that his Marleyan half-brother Zeke might be partly -- or maybe wholly -- to blame, but there's another more mysterious moment that provides a clue.
Picking up where Episode 9 left off, "A Sound Argument" features the current, chiseled version of Attack on Titan's central star imprisoned underground, staring into his cell's mirror over a sink. What's important to note about this scene isn't what we see or hear -- it's what's been left out of it. In the last episode, we saw Eren breathe onto the glass, as though about to write on it. We don't see whether he actually does or not. Though we're still in the same scene, Episode 10 seems to have skipped ahead a little in time, catching Eren in mid-conversation with... himself. In fact, he doesn't seem to notice that Commander Hange is standing on the other side of the bars observing him.
Hange queries why he's repeating the word "Fight" to himself, wondering if he's really talking to himself or believes that there's someone else (besides Hange) in the room or in his head. True to form, Hange continues to theorize, babbling out of nervousness perhaps until Eren grabs his superior through the bars. He points out that his consumption of the War Hammer Titan means he can escape from his solitude anytime he wants -- diminishing Hange's authority over him both verbally and physically. Hange laughs it off but is visibly shaken by the threat later on.
On the surface, the mirror scene serves to widen the growing gap between Eren and the rest of his supposed friends and comrades. He might be behind bars as punishment for acting out on his own and endangering lives, but his anger towards Hange isn't just teen brattiness at being put in detention, as the Commander accuses him of. The intensity of it, backed up by the sparks of a Titan transformation, offer another important insight into Eren's mental state. It seems that he hasn't just sided with Zeke because he has begrudging faith in his master plan -- Eren is doing his utmost at the moment to distance himself from the Survey Corps. He appears to have lost faith in their ability to make a tough call.
But the missing pieces of this scene, coupled with Hange's curiosity, should make it clear to Attack on Titan viewers that there's much more going on underneath. The series is nothing else but a masterclass in foreshadowing. Tiny details, from the tinned food with foreign labels Ymir discovered in Season 2 to more recently, the baseball mitt signaling Zeke and Eren's collusion, are intentionally easy to overlook at first but, once the pieces are in place, explosive in retrospect. The question is, then, who, if anyone, is Eren communicating with in the mirror scene?
By now, Eren can readily access the memories of two of the three Titan Shifters in his head, which is probably more than enough to give him a serious headache sifting through all the clutter. It could be that talking to himself is simply a byproduct of deep-diving into past inheritors' lives. This becomes even more complicated in the case of the Attack Titan, which has past and future recall. In the anime, we know next to nothing about how this future sight works, but it could well have influenced Eren Kruger's decision to select Grisha Jaeger, specifically, as the Shifter's next holder before Eren. After all, if you know what the future holds, you can either choose to make it happen or... not. Assuming, of course, that it's not a fixed point in time.
Could Eren have been making use of the Attack Titan's unique power in-between Episodes 9 and 10 of Season 4? And who -- or what -- is he telling to "fight?" Whatever the answer, there are a lot of reasons to believe it's more than just a one-to-one pep talk, or the dissolution of his mental health.