User blog comment:IamJakuhoRaikoben/Chapter 477: Transport, Review./@comment-24546844-20160314205730/@comment-24546844-20160315125501

To me his reaction and dialogue implied that he only noticed Mavis after casting his magic. The "there!" he said may mean that he only truly knew where she was after that magic bullet he shoot. If he could see her because of the bullet or he simply has some kind of "true vision", a fitting skill for an assassin, I don't really know. If I'm not mistaken not even Zeref can see Mavis though he can sense her.