Didn't sound like the rock met its mark. Then again, it was all the way over there, whereas Sirius was quite close in range.
"Why not?" he asked, playing innocent. Sirius only liked calling her his cousin because he knew how much she loathed any connection to him. He didn't care to be related to her himself, thanks very much.
"I doubt you're going to have a lot of friends on this island. You should rethink who you keep in your good graces."
He was mostly just saying this to avoid being pelted by a rock. Sirius could talk his way out of almost anything.
With Bellatrix, not unusually, it was a little more tricky.