Sirius watched the green alien and a grin spread across his face. So, he didn't like magic? Well, Sirius could have a bit of fun with that. And the alien did ask.

He pointed his wand straight at Brainiac and said "sonorus."

So Sirius was going insane? So what? That was even more of a reason to have a little fun. The next time the green man spoke it would sound like he was talking through a megaphone.