Peter seems to have realized he might have gone just a tiny bit too far and takes a step back, looking at her like he's expecting her to do something violent. This attitude is more in line with what he generally expects from her...but her insistence on this point is still weird. He wants to scoff at her, but for all that he's decided to trust Gabriel, it really doesn't take much for doubt to start seeping in around the edges again.

"...What do you mean, 'damnable,'?" he asks, still watching her like she's a snake poised to strike.