This happens in Act 3, during the ever-increasingly tense confrontation between Proctor, judge Danforth, Hale and Abigail outside the court. Hale, having iniitially supported the court, is by this time increasingly beset by doubts about the whole affair. He is now suspicious of the girls' claims of witchcraft and, like Proctor, he is beginning to realize that these accusations are based on private feuds and disputes rather than on supernatural events:
l may shut my conscience to it no more - private vengeance is working through this testimony!
He also voices his support for Proctor, and by the same token, he denounces Abigiail:
This girl has always struck me false!
However, Abigail, always ready to defend herself, interrupts Hale when he says this. By this time, her affair with Proctor has been publicly revealed (even though Elizabeth, through misguided loyalty to her husband, denied it) and now Hale is also denouncing her. She perceives therefore that the tide is turning against her and realizes that her credibility may now be seriously questioned. Therefore, she acts quickly to try and bring things back in her favour, by concocting yet another charge of witchcraft. She does this by interrupting Hale ‘with a weird, wild, chilling cry’, as she pretend to see a ghostly ‘yellow bird’.
Furthermore, Abigail blames the apparition of the 'bird' on Mary Warren, who, at Proctor’s urgings, had tried to expose the witchcraft charges as pretence. This turns out to be quite a stroke of genius on her part, as not only do her claims about the bird impress the (admittedly) easily-swayed Danforth, she also terrifies Mary Warren into deserting Proctor and rejoining her side. The result is that Proctor is officially charged for bewitching Mary Warren, Hale leaves in frustration, and Abigail’s reputation is once more assured in the eyes of the court. In short, she is left victorious.