It's from an old Jewish joke... This cloaked dark figure is walking down a dark alley, and he climbs up a fire escape, sneaks in a window, and walks down a hallway... He picks the lock of a door, and confronts a man in bed... " Ah, Pushkin, we meet at last!..." " I'm Pushkin the Dentist... You want Pushkin the Spy... He's two doors down..."