Julien was already trying to figure out how he was going to survive in Azkaban after they threw him in there for manslaughter, but the girl's voice and her seemingly un-crushed person assauaged his worries, though not his guilt. He was a little perplexed at how happy she seemed and wondered if maybe she'd hit or head, or whether it was just the relief from having escaped death by book-alanche.
He was frozen until he saw her bending to the pick the books up, reaching out to stop her doing so. "I-I suppose I could, I think- please, it was my fault, I'll clear this up." he insisted, flicking his wand towards the now semi-empty shelf with a quick spell that had the books fluttering harmlessly back, alphabetised properly.
He was happy that she didn't seem to want to break him in two for the trouble and was intrigued at her idea as it ran parallel to his own. "I was thinking about that but then I thought that the projection of the body would be open to too many factors too difficult to plan for, weight and height and so on, making the idea impractical as a safety device, but it was one of the first ideas I picked... up... too..." he trailed off, realising he was babbling and stopping himself. "Sorry. I got a bit carried away."