Here's an example of someone using that expression:
"The very fact that a prominent Irish republican can have a play on in London without ...." and the cops said, “Oh, you’ve got a tongue in your head after all!” They’re so smooth and slick in their job as professional interrogators.’ ...
What the cops mean is, "We've been asking you questions for five days and you haven't said one word." Then the prisoner says something about a play by an Irish republican. The cops respond, “Oh, you’ve got a tongue in your head after all!
It's something you would say to someone who has been silent for a long time who suddenly begins talking.
I hope this is helpful,