 "Eugenes Trick Bag", the updated classical piece at the climax of  the film, is largely based on Niccolo Paganinis Caprice #5.  Paganini, as the pervading myth has it, sold his soul to the devil  for his musical skills. Steve Vai (qv), as Jack Butler,  replicates Paganinis legendary rolling eyes, long unkempt hair and  gaunt stature.