Hermione rolled her eyes. At Ron this time because she wanted him to know that she thought he was being intentionally unhelpful. When he didn't care, she just naturally assumed than any answer he gave her was not fully thought out. Which, maybe, was a normal thought process for any time Ron gave her an answer. He didn't always think things through. But she had more faith in his reasoning ability than that.
"Ron, have you ever read or seen anything with zombies where dreams are a symptom? Where would you even get that idea? The two things are entirely unrelated. They aren't even infections in the same part of the brain. In fact, the part of the brain that controls sleep is unlikely to even be functioning in zombies because it also controls things like equilibrium and facial expressions - which zombies don't have." About six down in the pile of books beside her bed was a book on the different parts of the brain.