tirer les vers du nez

To coax a secret out of someone

Used when you coax information out of someone bit by bit, rather than them telling you outright.

À force de questions, elle a fini par lui tirer les vers du nez.

With enough questions, she eventually got the secret out of him.

Nobody is entirely sure. One theory points to old quack cures that claimed to pull worms from the nose to treat illness, another links it to the Latin verum, meaning truth. The phrase is attested since the 15th century, but no explanation fully satisfies.