She doesn’t fear him at all. Early in the play she’s worried that he’s too full of the “milk of human kindness” to commit the murders necessary to become king (and for her to become queen). If she’s afraid of anything, it’s that his soft-heartedness will keep him from the throne. What happens to her (and him) later on will show just how misplaced her fears were. Now go do your homework. Christ, isn’t schoo