Theo nodded; he was relieved the rats were still alive too, although he didn't hold out hope for that lasting. He didn't tend to hold out any hope in general though. The experience of someone being happy for him was new though and he tilted his head, unsure of Ernie's sincerity. He gave his friend the very unpractised benefit of the doubt though, the other guy hadn't steered him wrong yet. He was pleased to hear that Ernie hadn't had any problems today, but he struggled to hide the flinch when Ernie mentioned a world outside St Mungo's. He couldn't remember those days much, but he did recall falling into a hole in that place and not pulling himself out for some time; remembered that he thought that little room was his world.
He broke out of it when Ernie accepted the book, his expression a little bashful. "That's okay. You can keep that copy." he reassured, having a copy of his own at home.