The little maggot was pressing him onward, even after Zachariah had threatened to send Castiel upstairs. That sort of behavior might have flown with the Winchesters - clearly, it was something they prided themselves in - but it wasn't tolerated among their kind. There was a slight twitch to the smile cracked upon Zachariah's vessel's lips as he stared across the room at his brother; a smile, even a fake one, was hard to keep up when one wanted to do nothing more than grab someone by the throat and rip them to shreds. Castiel's behavior was more than unacceptable. He was supposed to be nothing more than a robot, quick to agree and follow through with the commands installed into his system. Zachariah was the one typing those commands into Castiel's mind. It was almost like he was sitting at a computer tapping words into the keyboard, only to have the screen before him screech "ERROR, ERROR, ERROR" in response. That in itself was incredibly frustrating.
"Dean Winchester needed to be motivated," Zachariah replied as stiffly as before. "Your progression at his side isn't going nearly as quickly as it should be." Reaching up, Zachariah straightened the collar of his suit out and turned away from Castiel, one hand dropping onto the long table that stretched along that side of the room. Fingers smoothing over the surface, Zachariah walked around to the end of the table and placed both hands along it's edges, leaning against it slightly as he did so. "He needs to be pushed in ways that you alone - clearly - are incapable of accomplishing. As do his friends. I thought that it would actually be very obvious to you." Zachariah flicked his gaze back to Castiel, a cold tone passing through his features. "It isn't, is it? I can see it in your eyes, Castiel. You're beginning to doubt." Zachariah drew in a breath that he didn't need, shaking his head quietly. "Such a shame. I had high hopes for you."
He was questioning him more than was necessary. It was becoming painfully clear that Zachariah needed to put him back in order. That supposed computer that he had been compared to had been corrupted with a virus: his exposure to humanity. The humans. His system would have to be wiped clean. It would be far from a pleasant experience for Castiel, Zachariah was certain of that.
At the moment though? He considered that as a good thing. He wanted Castiel to suffer. If only because he couldn't eradicate him just yet.
"This isn't acceptable behavior, Castiel," Zachariah said critically. "You know what I'm going to have to do about that, don't you?" There would be angels lying in wake. All Zachariah had to do was summon them over to drag Castiel back to the place in which he had been made.