While Sandro Botticelli is famous for mythological works like 'The Birth of Venus,' he was also a prolific painter of religious subjects. However, one of his most distinctive stylistic choices, particularly in his late works, was his use of a swirling, linear rhythm and emotional intensity that seemed to move away from the High Renaissance's focus on calm harmony and realism. Which of these terms is often used to describe this more agitated, expressive style seen in works like his 'Mystic Nativity'?