Why do the putnams start talking about witchcraft? what do they and others mention as signs of witchcraft?

In Act I of this play, Mrs. Putman and her husband are talking about witchcraft because their daughter, Ruth, is ill and they believe witchcraft to be the cause. Mrs. Putman had previously sent Ruth to see Tituba, who they believe has the ability to speak to the dead and is involved in witchcraft. They also mention that Betty's illness is a "stroke of hell."