Lady Macbeth:
Out, damned spot! out, I say!--One: two: why,
then, 'tis time to do't.--Hell is murky!--Fie, my
lord, fie! a soldier, and afeard? What need we
fear who knows it, when none can call our power to
account?--Yet who would have thought the old man
to have had so much blood in him. [Macbeth][V.i.16-21]
When you read these lines out loud or hear these lines being spoken or read aloud, does it convey something? Shakespeare makes a shift here, from the usual flow of speech sounds into one that is disharmonious, in order to indicate a change in mood and situation. Lady Macbeth, here is overcome by guilt and remorse for aiding and abetting in the murder of Duncan, and the speech here signifies her deteriorating mental health. The literary device Shakespeare uses here in his play Macbeth as well as in places, in his other plays, especially, in Tragedies, is cacophony.
Cacophony, in literature, is a combination of harsh-sounding words within a text. It is disharmonious and used to convey confusion, unpleasantness, annoyance etc. It is not dissonance alone but more. It includes dissonance as well as sibilance. Cacophony indicates a shift in mood or situation, using primarily plosive consonant sounds as well as other consonant and vowel sounds.