The two doors enigma

Sarah, after having realized that the labyrinth is constantly changing, finds herself in front of two gates protected by four guards: grouped in pairs, one upside down, holding a shield that hides the trunk of their bodies.

Sarah: Oh no! Someone has been changing my marks. What a horrible place! It’s not fair!

Bottom Red Guard: That’s right, it’s not fair! (Laughing with the other guards) But that’s only half of it.

Sarah meets the guards

Sarah: This was a dead end a minute ago.

Bottom Blue Guard: No, that’s the dead end behind you. (Laughing with the other guards)

Sarah: It keeps changing… What am I suposed to do?

Bottom Red Guard: Well the only way out of here is to try one of these doors.

Botton Blue Guard: One of them leads to the castle of the center of the labyrinth, and the other leads to…
Top Blue Guard: BAH BAH BAMMM…
Bottom Blue Guard: Certain death!

Guards: Ooooohhhhhhhh…

Sarah learns that she could be facing death

Sarah: But which one is which?

Bottom Red Guard: We can’t tell you.

Sarah: Why not?

Bottom Red Guard: Uh… We don’t know!
Bottom Blue Guard: But they do (looking at the top guards).

Sarah: Oh, then I’ll ask them.

Top Red Guard: Uh… No! You can’t ask us. You can only ask one of us.
Top Blue Guard: (Agrees) It’s in the rules. And I should warn you that one of us always tells the truth, and the other one always lies. That’s a rule too, he always lies.
Top Red Guard: I do not, I tell the truth!
Top Blue Guard: Ohhh what a lie!

Bottom Blue Guard: (Laughs)

Sarah asks her question to the Top Red Guard

Sarah: All right… Answer yes or no (asking the Top Red Guard). Would he tell me that this door leads to the castle?

Top Red Guard: Uh… (Thinks) (Consult the Bottom Red Guard) Yes!

Sarah: Then the other door leads to the castle, and this door leads to certain death.

Guards: Ooooohhhhhhhh…

Top Red Guard: How do you know? He could be telling the truth.

Sarah: But then you wouldn’t be, so if you told me that he said yes, I know the answer is no.

Top Red Guard: But I could be telling the truth!

Sarah: Then he would be lying, so if you told me that the answer is yes, I know the answer would still be no.

Top Red Guard: Uh… Wait a minute, (asking the Top Blue Guard) is that right?

Top Blue Guard: I don’t know! I’ve never understood it…

A scene from the movie Labyrinth…