It says, "the room is empty but for sunlight pouring in through two high windows in the black wall." It gives the impression of solemnity and depression, and also makes the small room seem claustrophobic so the girls have nowhere to escape.
This reflects the stifling society and the situation that the girls have got themselves into. Middle Mary immediately springs to her feet and protests in shock, pleading Abigail to stop with the deception and to tell the truth.
They act like bullies, ganging up on her because she is weak and the tension builds up, as Mary gets more and more distressed.
The girls start mimicking Mary, which is a typical playground-bullying device, which is guaranteed to undermine her.
Miller does this to create an atmosphere which is unhappy and depressing.
The tension is already high as the scene before ended with satanic accusations.
In the play Miller shows how the accusations affected everyone in Salem.
Miller creates a sense of tension by setting the scene in a "low, dark room." This room is quiet and gloomy as very little light is getting in.
Abigail targeted her as she chose to confess and she will do anything to get her way, as she is frightened that Mary would reveal the truth.
They then advance further to imitating Mary's actions - stamping feet and shaking fists, strengthening the tension, and maddening the audience even more with aggravation. Conclusion Hale leaves the court and the scene ends with Danforth shouting to him to come back, leaving a cliffhanger into Act 4.