what is alarming about how the mysterious being responds to Victor? How does it act, speak, and conduct itself?

Initially he is full of rage. The monster asks Frankenstein to alleviate his misery, and threatens to "glut the maw of death... with the blood of [Victor's] remaining friends" if he does not comply with his wishes.Then the monster changes his tonne. The monster eloquently argues that he is intrinsically good, full of love and humanity; only the greatness of his suffering has driven him to commit acts of evil. Though he is surrounded by examples of human happiness, he finds himself excluded, through no fault of his own, irrevocably excluded from such bliss. He implores Frankenstein to listen to his story; only then should he decide whether or not to relieve the creature of his agony.