Q: Given scene/plot descriptions from movies or TV shows, and given a specific question about the scene, summarize the question into a title
In The Exorcist, why does the demon that possesses Regan react to the "fake" holy water sprinkled by Father Karras? It's hard to believe that the demon mistakes the tap water for water blessed by a priest. It certainly makes the entity that much less frightening.
A:
Why does the demon that possesses Regan react to the "fake" holy water?