Macguffin

Macguffin's are often used in thrillers to sidetrack the audience. It often makes us forget the reason as to why all of the events we see unfolding actually happen. An example of this occurs in the film 'Birds.' The Macguffin would be the romance that begins to blossom between Melanie and Mitch which makes us almost forget that the main theme of the film is the birds which are attacking the town.
The effect of this is that we are drawn into the film further and then surprised with the memory of what is actually happening. This automatically intrigues the audience and keeps them hanging on to what's going to happen as an outcome of these unpredictable events.