Abigail's threats against the girls are taken seriously because?

The girls were truly afraid of her. She threatened them with violence,

"Now look you. All of you. We danced. And Tituba conjuredRuth Putnam's dead sisters. And that is all. And mark this. Let either of you breathe a word, or the edge of a word, about the other things,and I will come to you in the black of some terrible night and I willbring a pointy reckoning that will shudder you. And you know I cando it; I saw Indians smash my dear parents' heads on the pillow nextto mine, and I have seen some reddish work done at night, and I canmake you wish you had never seen the sun go down!She goes toBetty and roughly sits her up.Now, you—sit up and stop this!"