How do people watch movies? That is to say, what do they look at in a given scene, and what do they ignore? It's been a hard thing to study, at least until the invention of eye trackers that can pinpoint exactly what you're looking at.
So using some eye trackers, researchers had some viewers watch a scene from There Will Be Blood. They wanted to see what people focused on, what made them notice (or miss) continuity errors, and to generally see what they could learn. The study is in-depth, fascinating and well worth the read, so go check it out!
Here's the video showing what 11 people looked at while watching this scene from the movie: