What is Pearl doing during the sermon ?

"Little Pearl, meanwhile, had quitted her mother's side, and was playing at her own will about the market-place. She made the sombre crowd cheerful by her erratic and glistening ray; even as a bird of bright plumage illuminates a whole tree of dusky foliage by darting to and fro, half seen and half concealed, amid the twilight of the clustering leaves. She had an undulating, but, oftentimes, a sharp and irregular movement." Chapter 22