Diego said:

And like a lot of other things in the prequels, he's only there so we can have yet another lightsaber fight, cause you know, having three fights in a movie is not enough, you need four or it gets boring.

I fell asleep during Obi-Wan's fight with Grievous.

I used to stay up all night watching the trilogy or playing the games. Then I fell asleep in the middle of the day watching a brand new Star Wars movie. That's when I knew all the fire had gone out of the relationship and we were never getting it back.

Fortunately, my brief nap left me refreshed for lightsaber fights #3 and 4.

None of this is really scientific of course. We could set up cameras to watch people's eyes while viewing the movies to track their attentiveness, or draw blood for stress hormones and endorphins after key scenes. We could also use EKGs, EEGs, plethysmographs, etc. to monitor physical arousal. Familiarity or recall can be measured by simple surveys, distributed at random to a large enough population. Advertisers and anti-advertising advocacy groups frequently use such surveys to measure mascot familiarity among children.