What is an example of motif in the motion picture, Witness for the Prosecution?

Throughout the film, there are always interruptions. The first comes while Robarts is talking with his nurse and servant. Mayhew knocks on the door and demands to see Robarts concerning a murder case. All the drama and action in the film begins because of one simple knock on the door, one interruption.

Later, viewers also see numerous other interruptions that introduce us to new characters or prepare us for a later event. For example, when Christine interrupts Robarts's conversation at his office, we are suddenly thrown for a loop as we see her cold disdain for her husband. Because we are set up to dislike her, the ending comes as an even greater shock for the viewers.