spoke with a serrated tongue

[Coffee Break]

I encountered the sentence "spoke with a serrated tongue", but am struggling to understand it. Could you please let me know what it means? Here is the excerpt:

Then she told me: “Just don’t make me think this is happening in my head. Because I know you,” she said. “And I know myself. I want this, but I also know what you’ll drive me to do, and I pray, pray, you don’t.” I had no idea what she meant. “Don’t you have any trust, any faith?” I asked. “None.” In moments of extreme tenderness she spoke with a serrated tongue.

It occurred to me she must have thought the same of me. Had she asked me if I trusted anyone, I would have said the exact same thing.

- André Aciman, Eight White Nights, Fifth Night

This is a novel published in the United States of America in 2010. It is narrated by a nameless male protagonist. He meets Clara at a Christmas party in Manhattan. Four days after the party, the protagonist is at the bar with Clara. After they kissed, Clara is talking to the protagonist that he should not make her feel like this is happening in her head.

I wonder what the underlined expression means.
I first thought that she might indeed have a serrated (saw-toothed?) shape of a tongue, but then I guessed, "tongue" might here mean "language"...
But these are just my guesses, and I am still confused as to what that means.

 

[Tarheel]

I don't know why you think it means anything. It seems to be a phrase the author made up. You will have to find the meaning within the context of the story. (It does seem to be an allusion to speaks with a forked tongue.)

 

[Skrej]

It's a variation on the phrase 'sharp tongue'. Instead of merely being sharp, her tongue is also (metaphorically) serrated. Serrated blades are designed to help the knife cut better, especially through certain types of materials.

The use of 'serrated' serves to illustrate that her cutting tone is even more acerbic. Note the juxtaposition of speaking thusly in a moment of tenderness.

 

[Coffee Break]

@Tarheel and @Skrej,

Thank you very much for the explanations.
So it is a variation of other idioms, such as "forked tongue" or "sharp tongue"!
And here "tongue" does not literally mean the organ of her body, but means "language.

If her language is not just sharp but "serrated (having a saw-toothed shape)", it would mean that her language is extra sharp and acerbic.

I learned many things all thanks to you. I sincerely appreciate your help.

 

[Tarheel]

@Coffee Break She is given to making barbed comments.