"Of course, dear." Narcissa’s smile neared a smirk. "Are you familiar with the myth of the Dioskouri?" Hermione nodded - the twins that made up gemini. "As Castor and Pollux were combined into one body, the ritual combines two wizards - though maintaining their separate bodies. Each carries a small part of the other, untouched by any outside forces." She paused for a sip of tea. "Therefore, any blood magic performed on a wizard in a Dioskouri bond would only result in a weak pull, or none at all."