There's a scene from a movie I saw many years ago that has stuck with me, but I don't know what the movie is.
Scene setting: Dungeon or other locked area (treasury maybe?) in a castle. A man and maybe accomplices want to gain entry. There's a guard inside, and people on each side of the door can talk to but not see each other.
It seems like it would have been a Peter Sellers movie, but I've looked through his credits and nothing seems to match.
Dialog goes something like:
Guy: open this door!
Guard: Who is it?
Guy: It is the king crown bearer
Guard: Who is that?
Guy: That is me
Guard: And who are you?
Guy: I am the king crown bearer
[...this goes on for a while...]
Guard: If I open this door, whose visage will I see?
Guy: You will see my visage
Guard: And whose visage is that?
Guy: The visage of the king crown bearer