“The pure-blood families are all interrelated,” said Sirius. “If you’re only going to let your sons and daughters marry purebloods your choice is very limited, there are hardly any of us left. Molly and I are cousins by marriage and Arthur’s something like my second cousin once removed. But there’s no point looking for them on here — if ever a family was a bunch of blood traitors it’s the Weasleys.”
