Double, Double toil and trouble'
Lot of plosive sounds 'o' 'e' 'b' create a thumping sound almost as if an earthquake and are shifting natural order emphasising their undeniable power.
Furthermore Repetition of 'double' hold great importance serves as a reminder that their speeches are full of intricate double meaning contradictions and deception.
Rhyming couplet make it like a children nursery rhyme and paint mockery of the witches showing only weak fall for the witches power.