In the exorcist how did the demon greet the exorcist?

In "The Exorcist," the demon, known as Pazuzu, greets Father Merrin with a chilling sense of familiarity. During the exorcism, the demon taunts him, referring to his past experiences and knowledge, which highlights the personal nature of their confrontation. This interaction underscores the demon's malevolent intelligence and the psychological battle between good and evil.