Nancie Atwell, one of my pedagogical heroes, talks about getting in "the zone" while reading books. Being so involved with the story on the pages in front of you that the classroom surroundings just fade away and you become part of the story.
I frequently see this with my new class of students. I often find the bell ringing and having to shoo the kids out of my room because they just won't put their books down. I guess there are worse problems to have as a teacher.
Nowhere was this reading zone made more clear to me than the other day when I came across one of my 5th grade students (I teach mainly 6th grade, but I have one class of 5th grade reading) sitting at the round table with my stuffed frog on his head. He was not doing this to be funny or draw attention to himself. In fact, he was sitting this way for quite a while before I even noticed. That's what I call being in the reading zone: being so engaged in a book that you don't even notice that you've got a frog on your head.