He notices the little flick of wordless magic and it's the first time he thinks this might be a problem. Doesn't let it show because at least she's there on the couch, close to the snake even if she's not close enough to be bitten, yet. He sits beside her because proximity to the creature makes Sirius so much easier to control.

Because Sirius is fighting, now; kicking just slightly against where his mind is caged at the consistent threats to Lily's life. It's growing very frustrating. He manages (only just) to keep the expression out of his face.

Lets, instead, something that captures the smugness just slightly slip out instead. Of course that was something Black would've tried to keep from him. Probably thought it would keep her safe.

"I'm sorry if I made you think that I wanted to be found," he says, and there's something syrupy sweet about his tone that Sirius never, never uses. One hand is reaching out to her to rest on her knee, and oh, Sirius is seething. It's going to be such a pleasure to break the both of them, "But I got what I wanted from you, Lily. I've found something better, now. It's a shame that things are such a problem at home with James, but--" A shrug, "--I can't help you with that, I'm afraid. We've all got to go our own ways, now."