Mary Warren's exact words in this instance are:
But, Mr. Proctor, they will not hang them if
She says that those who have been accused will not hang if they confess.
She says this after she returns from court where she had been the entire day, providing testimony against those who had been accused of witchcraft. Mary had just implicated Goody Osburn (a beggar) by informing judge Hathorne of her 'mumbling.' She had reported that she had once suffered a bad stomach ache when she refused Goody Osburn 'bread and a cup of cider.' Goody Osburn had then mumbled something and Mary was suddenly overcome with pain.
The court did not even attempt to ascertain the facts and asked accusatory questions of Goody Osburn.
Mary Warren: And so I told that to Judge Hathorne, and he asks her so. “Sarah Good,” says he, “what curse do you mumble that this girl must fall sick after turning you away?”
Unfortunately for the poor woman, she was caught in a lie when she mentioned that her 'mumbling' was just her saying her commandments. When she was asked to recite these, she could not remember a single one of them.
It is clear that Mary had become overwhelmed by the entire dramatic display put on by the girls. She had sort of become part of a conspiracy, led by Abigail Williams. The girls were pointing accusatory fingers at many innocent people for two principal reasons: firstly, they were afraid of Abigail Williams who had threatened them should they not follow her lead and secondly, they enjoyed the power they had and relished the opportunity to implicate especially those with whom they had an issue.
As it was, those who had been accused and arrested on charges of witchcraft could only save themselves by confessing their allegiance to Satan and that they had performed witchcraft. If they refused, they were hanged. Mary has informed the Proctors that thirty-nine had already been arrested and that some would only spend some time in jail because of their confessions.
Proctor: Mary. She halts. Is it true? There be fourteen women arrested?
Mary Warren: No, sir. There be thirty-nine now -
... Sarah Good will only sit in jail some time.