MacGuffin

Alfred Hitchcock was a very successful film director and producer and was often nicknamed "The Master of Suspence", he pioneered many techniques in the suspence and psychological thriller genres. He created the term MacGuffin which means a plot. Device with little or no narrative explanation. This is to attract he audience in the first a act to allow them to become suspicious of things going on. It is commonly used in thrillers as his can be done quite easily to keep the audiences attention. It has been achived in many films from North by Northwest, Star Wars, the 39 steps and many more. The Princeton WordNet simply states it as "a plot element that catches the viewers' attention  or drives the plot of a work of fiction"