Interesting Little Test

There are these two people, lets call them person 1 and person 2. Person 1 was using StumbleUpon and came across a silly game/test thing. More out of luck than anything, they get 10/10. When person 1 is hanging out with person 2, person 2 finishes up watching an episode of Dexter, which is a show that they love but person 1 is only familiar with the gist of. This reminds person 1 of the test, and person 1 shows it to person 2. Person 2 takes it, and they have the following conversation:
Person 2: I got a 4 out of 10.
Person 1: Remind me never to trust /your/ instincts.
Person 2: Well, what'd you get?

Person 1(not wanting to embarrass person 2); Um... 6/10, I think. So, also an F.
Person 2 (jokingly): I'm actually kind of relieved. I mean, if Dexter is to be believed, maybe it's a good thing neither of us have that "instinct".
Person 1: Haha... yeah. Ha...

If you want a link to the test, here it is: http://www.malevole.com/mv/misc/killerquiz/. It's more fun when you don't recognize any of the pictures (I know I didn't), but I'm sure some of you will.