Castiel's expression flinched slightly every time Dean said 'pop.' He was by now used to the man's hastily chosen expressions, but he wasn't sure that it was really necessary to make it sound like he was microwave popcorn. "We confronted Lucifer?" he asked, rhetorically, marveling at the idea. Castiel was not even close to an archangel, being more of a warrior in rank and file and Lucifer being an Emperor General with more experience than any being Castiel knew of. He was, rightly, awed.
"People don't," Castiel agreed. "God must have returned me to you." He looked steadily at Dean, patient for an explanation. "Why?" Obviously there must be some situation, something Dean must have done, to warrant a guardian's return.