Idea Influence - Paranormal Activity 2

When we watched the trailer for Paranormal Activity 2, and having seen the film in the cinema, the slamming of the door (0:37 seconds - 0:41 seconds in the above trailer) really scared the audience as they did not expect it and it had been quiet before this. The idea of a surprise noise or action would be something we may look into inclusing in our horror opening.