"The sisters never thought their secrets would get out - having it used on them was not a reality they had thought of. Clever though they were, the house of Black is blinded by pride." She paused. "There is an old bonding ritual that was said to protect two parties against any sort of dangerous blood magic, but it became a retired practice due to its irreversibility." Hermione saw Malfoy shift uncomfortably in his seat as his mother spoke. "There is no way of knowing or testing it, but if anything could protect against a blood curse - it would be that."