Walter said nothing to regard the woman's answer. Instead he just watched her like a wolf eying it's prey. His demeanor was eerily calm. "Yes, it would be a shame if you were killed by a monster. There are so many unworthy 'monsters' that could kill you at any moment." He explained this with a smile.
The fact that her hands had transformed amused him to a degree. Instead of mentioning anything though he simply pulled out the knife from his pocket, twirled it once, and had it clutched in his hands with the blade pointed right at her. "Tonight you'll be killed by the Son."
After he said that, Walter quickly disappeared in the darkness. Having become a shadow he was soon right behind Katherine with his knife hand close to her throat, but he was still in shadow form. He didn't become a physical form just yet, but waited for the woman to make her next move. He always loved the thrill of the capture.