Answer:
Mary Warren is perpetuating falsehood when she aligns herself with Abigail Williams and the other girls, making her complicit with their false visions and accusations of witchcraft. Specifically, once she is convinced by John Proctor to tell the truth about the girls' accusations, she is manipulated by Abigail into recanting her confession and accusing John Proctor of attempting to coerce her into a compact with the Devil.