Argentia kept her eyes on the door of the study when she handed the book to Victoria. She sensed Aran was gone. The reason they both can sense this snake in the shadows was that Argentia carried an amulet that was charmed and inscribed by Oleksiy Vlad for her. In case anyone dared to spy on her, that amulet will turn hot.
The day always wore the amulet on her body. So when she was reacting, the amulet suddenly turned hot. She knew it was Aran. Victoria meanwhile was pure blood and her senses were stronger than the normal vampires. This time she was excited and let her guard down that was why she missed Aran's presence.
Sensing that the snake is gone, he probably thought that the mother and daughter are talking about some girl's stuff. Argentia asked in a low voice, "Did you really feel your heartbeat for Bones, the hunter?"
