What does Levi’s big flare gun shot set into motion? Well, in the immediate moment, not all that much; it’s only an acoustic round that doesn’t seem to affect the She-Titan at all, but could serve as a signal for the soldiers ahead of them, as well as wiping everyone’s slate clean, so to speak, and focusing them.
But the more Eren focuses on what’s behind him—scouts engaging the Titan and getting killed, while he runs away—the more upset he gets, to the point he’s ready to bite his hand and become a Titan himself so he can stop the killing. Levi, looking ahead the whole time, doesn’t discourage him from this. Rather, he tells him to make his own choice, though Petra begs Eren to believe in her and his other comrades.
Those words—“Believe in us.”—triggers a flashback, which is another suspension of the momentum of the present events, but actually turned out to be a worthwhile detour. When Eren climbs down a well to test his Titan-transforming powers, biting his hand doesn’t work. Levi tells him not to sweat it, and they have some chow.
But as Eren reaches for a spoon that’s just out of reach, the Titan transformation occurs, as he unwittingly creates a partial Titan torso and arm grasping that spoon. All of a sudden, Eren’s comrades draw their swords and start yelling, ready to kill him if he so much as flinches. The sense of cascading fear and mounting chaos in this scene was quite palpable.
Eren tries to de-escalate by shouting “Be quiet for a second!”, but he’s really saved by an elated Hange Zoe, whose mouth is literally watering at the chance to see Eren’s ability in the hot, skinless flesh. Ironically, it’s Hange’s crazed, reckless thirst for knowledge and unapologeticly light mood that defuses the tense standoff. And Romi Park is immensely entertaining in this role.
An assist goes to Levi, who stood between Eren and his trigger (or rather blade)-happy officers and insisted they all basically chill the fuck out. No one acts in the time between Eren’s transformation and Hange’s arrival because the others are heeding their Captain, even if the compulsion to act decisively without thinking too much is strong.
In fact, those instincts are one of the very reasons Levi chose them for his unit. None of the men or woman directly under Levi can be said to be like Armin; they’re not overthinkers. If they see an imminent threat, they don’t assess; they act. But another reason he chose them is their unswerving loyalty. When Hange determines Eren’s actions were involuntary, they know when they’re wrong and that they were threatening jerks to Eren, and not only apologize, but bite their own hands.
Would they act exactly the same way as they did if the clock was turned back (as tends to happen on this show) and they faced identical circumstances? Definitely, but that’s not going to ever happen, because now they know a little more about Eren and his ability: he only transforms when there’s a specific purpose to it, whether it’s protecting his friends from a cannon, plugging the gate, or reaching for a spoon.
That night when Petra and the others bite their hands pledge to believe in Eren, and urge him to believe in him; that’s the end of Eren’s deliberations. Petra’s look up top is the same as the one from that night, an earnest plea for him to put his trust not only in himself, but in her, and Levi, and the rest of his comrades. Rather than transform, with the purpose of beating the She-Titan, he decides to keep racing forward on his horse. He’s growing a lot on this mission…without having to grow into a Titan.
His faith in his comrades and the Scout Regiment in general pays off, as the She-Titan, having been harried by several scouts who gave their lives to enable Levi, Eren, Petra & Co. to stay just ahead of her, is led straight into an elaborate trap consisting of hundreds of restraining wires that stop her in her tracks.
This was Erwin’s plan all along: using Eren to draw the She-Titan into captivity. She’s covering her nape, but they believe someone is in there (probably someone with that same hairstyle, I’m thinking), and they’re itching to get her out of there so she can answer for what she’s done…whoever she is.