"Then prove it," Cas said mildly. "Open your eyes and tell me to my face I am not real." He didn't let go of Sam's hand, his grip tight. "Tell me, Sam. On my terms. If I am not real you have lost nothing." He wasn't sure how capable Sam was of reason but he had to give him the credit his intelligence usually won him.
"Open your eyes. Tell me to me face." He stood calm, ignoring the shadow of his brother as he taunted Sam, his steady gaze a contrast to Lucifer's cold bloodlust.