He jumps back at first, not realizing that the intruding animal is, well, just a rabbit. It's a surprise to see one so apparently unconcerned by human presence.

It's even more of a surprise to see it join so many more rabbits clustering around another boy. How does that happen?

"...Are they yours?"

Is the boy some sort of rabbit farmer? But then again, he seems baffled by this as well.