He'd finally done it. He'd finally gone and fucked himself just like he'd known he would this whole time. Blanche is right there, and he's been in this situation before. There's no getting out. There isn't.

The panic is thick, and for a moment it's so bad that he almost just wants to give up without trying. It'd be so much less painful than struggling to the last moment, like he had before. But something about the lure's effect on him causes him to endure. The part that speaks to what's left of his love and his duty, and allows him to be angry at what's been done instead of bowing to the fear.

While Greg focuses on the Doctor, Sans appears off to the other side with blasters in tow. He starts off on a high note, by torching Blanche (or where he was standing a moment before, anyway) and the table he was sitting at.

Then, in that moment of distraction, he tries to bend the gravity around Greg and smack him down hard enough to interrupt his playing.