what does Othello think while watching desdemona sleep?

Othello enters Desdemona's room while she is asleep; and though she is beautiful, and appears innocent, he still is determined to kill her. He justifies this with images, metaphors, and ideas of her rebirth after death, and though his rage is softened, he is still much mistaken about her.

Othello's farewell to Desdemona is a return to his former eloquence, though it is also a farewell to his own peace and his life. Though he believes Desdemona's soul to be black, he can only focus on her whiteness; he pledges not to mar "that whiter skin of hers than snow," although he is determined to take her life. The metaphor highlights Desdemona's innocence, as does comparing her to a "light" to be put out. There is irony in Othello's references to Desdemona here; he describes her with words that suggest her brightness and innocence, yet he is determined to condemn and kill her.