If you knew the answer then why would you look. The fact that a person looks they are not confident in their own answer.
I still think that sam4321 has a good point. I can prove it from experience – in high school, after every test, my friend and I would go over all the questions together, just to make sure we got the same answers. There’s just some subconscious urge to second-guess yourself. And it’s a little bit iffy to indulge in that during the time construct of the test…