‘Scorpions’ are seen as malign creatures associated with treachery and poison
Scorpions are nasty creatures and the metaphor shows how evil Macbeth has become.
It is as if the witches with their morally undermining chants, ‘fair is foul’ have violated the sanctuary of Macbeth’s head and are now taunting his sanity with haunting images and guilt
"full" = an excess of mental fragmentation = nihillstic
