Hester notes in chapter 14 that the calm, quiet, and studious demeanor of Chillingworth is now gone. Instead he has an "eager, searching, almost fierce, yet carefully guarded look." She notes that it looks like there is fire in his soul and he seems filled with blackness. Basically, because Chillingworth has committed himself to revenge and to studying a man whose heart was full of torture (Dimmesdale), he has transformed into an evil man. The novel describes him as being a fiend or devil.