You can beat her and bind her for speaking any thing but a few key words.
But the best thing in the world is reducing your slave's vocabulary to 3 words without ever saying a word.
There's nothing like it when the only thing she can say is, "Oh God! Oh Fuck!"
It is so satisfying to see her reduced to a primal state by hitting her so hard with my unrestrained, full force sexual energy and just fucking her hard.