ari

In the Green Witch arc, Sebastian nearly aborts the contract and eats Ciel's soul, under the pretense that Ciel had abandoned his revenge and therefore violated the terms they'd agreed upon.

However, when Ciel directly accuses him of "seriously" (本気で) trying to eat him, Sebastian corrects him, saying he was about 90% serious.

But what does 90% serious mean? He either intended to eat Ciel or not. Did Sebastian mean that he was 90% certain he intended to eat Ciel, but wasn't sure if he would follow through at the last moment? Or that if he were 100% serious he would have gobbled him up immediately, but because he was only 90% serious he gave him a chance to change his mind about abandoning revenge?

In either case, it shows that he has changed (if only a little) since the beginning of their contract. Immediately after Ciel offically became an earl, around two months into their contract, Sebastian tempted Ciel into giving up on revenge. He didn't warn Ciel that this would count as a breach of contract.

If Ciel had given in, even for a moment, Sebastian would have ended him right there. This is Sebastian being 100% serious about eating Ciel.

Now, more than three years later, when his master is incapacitated, Sebastian's immediate concern is trying to fix him.

After the first time Ciel rejects his presence, Sebastian returns to the forest to investigate. He sends a sample back to England and, knowing there's nothing else he can do at that point, begins serving Sullivan in the hopes that she will fix his master.

She believes that what Ciel needs is time to recover, and Sebastian seems content to wait it out.

Although he assigns Finny to care for Ciel and devotes his own time to investigating the case and serving Sullivan, he still occasionally checks in on his master.

When the "wolfman" attacks Ciel and Finny, Ciel starts demanding to go home.

It is because of these demands, and not his own impatience, that Sebastian suggests "shocking him out of it."

It is Sebastian's duty as a butler and contracted demon to fulfill his master's wishes. However, Sebastian knows that what Ciel wanted, when he was in his normal state of mind, was to finish the case he had been assigned. He would hate if Sebastian let him give up and go home.

Tanaka assures him that acting hastily would only makes things worse, and that they should continue to wait and let Ciel recover. Sebastian accepts this because he knows the situation is beyond his experience and he values Tanaka's wisdom and insight.

He continues observing Ciel, who doesn't seem to be improving.

The situation rapidly unravels and Sebastian realizes his last chance has arrived to snap Ciel out of it before they are forced to leave.

He first tries being stern and telling Ciel the facts: if he doesn't get his butt out of bed immediately, they won't be able to finish the investigation for the queen.

When this doesn't work, Sebastian escalates to "shocking him out of it." He tells him that because Ciel is giving up, Sebastian is allowed to eat him. He tries to shame him into snapping out of it, saying how disappointing this ending is and that it renders all of the deaths along the way pointless.

This causes Ciel to truly assess whether he is committed to the path of revenge. He comes to the conclusion that he is, and the intensity of his determination snaps him out of his triggered state.

If Sebastian was 100% serious about eating Ciel in this scene, he would have done it before this point. He would have taken advantage of Ciel's altered mental state and eaten him immediately.

When Sebastian said he was 90% serious about eating Ciel, I believe he was being sarcastic. If you're not 100% serious about doing something, you're not actually serious.

He never intended to eat Ciel. The whole scene was an attempt to force Ciel to return to his right state of mind so that he could finish the mission.

Sebastian wouldn't have eaten Ciel's soul prematurely because he no longer wants to. He's known Ciel long enough to believe that his soul, when he achieves his revenge, will be the best he's ever had. He's invested too much time and effort to not finish what he's started (sunk cost fallacy?).

More importantly: Sebastian is enjoying himself.

When Ciel orders Sebastian to destroy the poison gas facility, the earl tells him he can act as beastly as he wants while doing it.

While carrying out his order, Sebastian reflects to himself:

Sebastian is saying that if Ciel wants him to behave like a beast he will oblige, but that Ciel is wrong in assuming that Sebastian's greatest pleasure is acting on his beastly impulses.

Sebastian says that his foremost amusement at the moment is his interactions with Ciel, "so it would not do to act on impulse and behave like a beast."

Sebastian isn't talking about indulging in violence here. Mere minutes before saying this, he had acted on those impulses.

The impulse he's referring to is his hunger for Ciel's soul. The two panels right after the quote show this.

The image of Ciel wrapped up is showing the "game" theyre playing, with all of its highs and lows. The panel of Ciel accusing him of trying to eat him is showing the beastly impulse that Sebastian must not indulge so they can continue the game.

All of this makes me believe that Sebastian did not intend to eat Ciel at that moment and was only using the fear of that possibility to shock Ciel into action.

He doesn't want the game they're playing against eachother to end, at least not yet. This isn't because he likes playing with his food or has discovered a lifelong passion for buttling. He likes the game specifically because it's Ciel he's playing against (with?).