Movement in general, not just rocking but tapping a pencil, moving the chair, walking around, doing cartwheels, or whatever... movement.
Looks a bit strange to me! Is this Sunnah? Doesn't one get a headache, dizzy head, backache with all that rocking? You wouldn't read a normal book like this would you... How do you keep your eyes on the Arabic text? It's not something I do - but if you can give me a source for it - I will start doing it.