The look on Gabriel's face made Cas suddenly uneasy, enough to unconsciously take a step back. Considering that the last time he had pissed off an archangel he had gotten blown to pieces, again, the movement had been a purely kneejerk reaction -- but the unease was short lived. Recovering quickly, Castiel stood his ground and watched the displeased man before him with the same sort of caution one watches an animal that looks about to attack.

This was indeed his big brother. The greeting was indication of that. Trying to make sense of what was happening, Castiel fell momentarily silent.

"How is this possible?" Honestly, he wasn't sure exactly what was happening anymore. Gabriel was a master of trickery, but even he wasn't possible of such an illusion. Was he? No, of course not. Castiel didn't know. "Lucifer struck you down. You've been dead for months."