The Ghost...
*SPOILERS*
One thing that has really been bothering me since seeing the movie last night. We see the ghost (presumably the ghost of Glick) throw Caity around the house like a ragdoll. So why would the ghost not just kill Judas when it clearly has the physical power to do so? The spirit could also have easily prevented Judas from killing Caity's sister and the others.
Personally, I find this to be a fundamental flaw in the story. It doesn't make sense.