I don't know.
4 seconds sound clip from the Labyrinth (1986) movie soundboard.
You can hear this line at 00:28:12 in the Blu-ray version of the movie.
Quote context
[...]
- All right. Answer yes or no.
- Would he tell me that this door leads to the castle?
- Yes.
- Then the other door leads to the castle and this door leads to certain death.
- Ooh. (2)
- How do you know? He could be telling the truth.
[...]