Arthur thinks about all the guns he still owns and about how he could just kill Bill or permanently incapacitate him but he doesn't say any of that out loud because that would just upset her. He also doesn't say that he doesn't believe someone like that can be reasoned with, so the curse would have to be permanent, but maybe if she tried to talk things out with him in a situation where he couldn't hit her she'd actually see what a sad coward he is.

He keeps quiet because he has a lot of these feelings that he can't say out loud, opting for sipping his coffee and settling back in at Eames' side instead.