Zhenya thought about that one. Why would someone prefer a physical silver shield over a different one. Her eyebrows were pulled together in thought, and finally, reaching a silly conclusion, she raised her hand.
"Professor, I… don't know much about them at all but V-vampires are… sensitive to silver, aren't they? Or maybe Werewolves. Perhaps some people might use a silver shield against these creatures to ward them off, because they know it will naturally work against them, more than protego, or any other shield charm." IT wasn't much of an answer, Zhenya realised it might even be complete nonsense, but it was the only answer she could think of.