how does danforth confuse mary warren?

When Danforth continuously accuse Mary Warren of lying regardless of what she says, the girl becomes upset, frightened and confused.

Danforth, containing himself: I will tell you this - you are either lying now, or you were lying in the court, and in either case you have committed perjury and you will go to jail for it. You cannot lightly say you lied, Mary. Do you know that?

Mary Warren: I cannot lie no more. I am with God, I am with God.

But she breaks into sobs at the thought of it, and the right door opens, and enter Susanna Walcott, Mercy Lewis, Betty Parris, and finally Abigail. Cheever comes to Danforth.