I think my arm will be alright. Playing Quidditch toughens one up, and it's already getting better. It's very decent of you to be concerned, all the same.
Quite right! If neither of your parents has magic but you do, it is because one of your great-grandparents was a wizard but married someone who wasn't, or something of that sort, and you were lucky enough to have that magic passed down to you. It is why it is very important for those of us from magical families to marry into other magical families, to make sure the bloodlines stay strong and our children are magical too. It is almost the same as encouraging certain traits in animals, yes.
Have you been here more than once, then? I think it's awfully courageous of you. The first time I left home it was to go to boarding school, and I was eleven, and I knew exactly when I'd be back. This place is far more uncertain. I shall have a dog of my own when I am a little older. We can bring cats to school, but not dogs, and I don't care much for cats. Aren't there cats and dogs in America, then?
I will talk to them, if I meet them. What's your name? You can call me Black; all my friends do. I can show you some flying tricks of mine too, if you like - once I've properly repaired the broomstick, naturally.