"Keep it that way. If I find out you ever do I'll show you no mercy."

It is a somewhat empty threat since she won't kill you or even try-- though she will make you regret it to the utmost, and she will definitely tell Marco when he returns. Perhaps that will be the only thing she will tell him when he returns. Blind idiots who discover secrets are sometimes even more dangerous than intelligent ones. He can be a puppet for anyone.