In Act One, what motivates Tituba to suddenly offer names of alleged witches after having denied being under the spell of the devil?
Tituba, a slave in the Parris household, has no power and is the most susceptible to punishment when people start to make accusations of witchcraft. Initially, Tituba and the other girls, led by Abigail, maintain that when Parris caught them in the woods, they were only dancing. But when the adults start to speak about witchcraft, they bring in Reverend Hale, an expert on witchcraft, to investigate. Hale begins to question Abigail, and in order to save herself from suspicion, she accuses Tituba of working with the devil and making her drink blood, among other acts. With this, Hale turns to Tituba and begins questioning. As he does so, Parris says to her, "You will confess yourself or I will take you out and whip you to your death, Tituba."
At this point, Tituba likely realizes that she has little choice but to confess. It doesn't matter that she was not involved with the devil; she is a slave, and the moment Abigail decides to accuse her, she is considered guilty. If she stays with the truth, she will die. When Hale then turns to her and offers her the opportunity to confess, she knows confession equals protection, and she makes the choice to save her own life.