Melon is 瓜 (guā), but 麻瓜 (má guā) is a transliteration of "muggle" by the looks of it. Could read as numb melon or something.

But returning to this comment what I mean is I can't find the first book in Mandarin, i.e. in Simplified Chinese... I think most people buy that and leave the rest which means it's much harder to find the first book in the UK. And that just won't do.

I'm not sure if Vernon makes drills or not in this translation, but I'm hoping the meaning is preserved.