[Oh, he stops just about instantly. Demon senses must be blunt in comparison since until half a second ago he didn't have an inkling something like this was around. Well.]
My, my. [He tilts his head to the side slightly, not turning around.] Quite an astute observation. It's commonly known as a briefcase.
[He's carrying one of those, see? Only once he's said that does he turn to look at Castiel, smiling broadly.]