The general mood of the movie is gray and stark, but not necessarily dark. The exorcism scenes are very dry and almost clinical in feel, probably because the director wanted to portray that the girl was suffering from a medical malady rather than a spiritual one.
There are several scenes wherein the girl has epileptic episodes where she becomes very frightened and hears voices. These usually end with her collapsed on the floor.
A girl locks herself in a kitchen and starts screaming and throwing things.