Her change in demeanor isn't instant. She has to take a moment to process it and he can probably enjoy the way her eyes widen and lips pull back in a snarl. Her whole body shifts from neutral wariness to on the edge of leaping and tearing out his throat.

"I knew you were familiar." She whispered harshly, "I knew. You fucking bastard."

She hates herself for reacting to it at all. It's what he wanted. She knew that. He wanted her to react like this and she is but she can't help it.