Mention of Rodolphus brought up the very real fear that he was about to betray her location to the horrible wizard. Was that why he was there in the first place? To figure out where she'd gone running? Rodolphus might have been an exceedingly patient man, but he had his limits. It was imperative to him that he complete whatever it was he'd been planning with Hermione. He might allow her to lull herself into a false sense of security for a little while. Eventually he'd strike back again.