Ambush as strategy to know a persons real thinking

To know what or how a person is REALLY thinking  - take them by surprise !
Ambush them in the gulch where they are least expecting it !

Once upon a time , a man came to the court of a great King  and displayed an  ability to speak many languages , fluently .
The court was amazed and the King  got many people ,whose native tongue was different, to speak to the man . He replied each one in their own tongue down to idiom and syntax.
On being asked , several times , the man refused to reveal his origins.
Intrigued , the King said he would offer a large fortune to any one who could discover the secret .
Many clever people approached the man himself and offered him a ' cut ' if he made them the messengers of the answer. He refused !
Then a clever one sneaked into the linguist's chamber in the early hours when he was fast asleep and sprinkled some water on his face .
The man was startled out of slumber uttering  who's that's and what's that's ( including some unprintables ) BUT THEY WERE IN HIS MOTHER TONGUE ! His secret stood revealed !
So while it's not advocated that we go around sneaking into bed chambers sprinkling water on people sometimes it's necessary to catch people with their mask off and defenses down  to know their truth.