Making the magic of the "Harry Potter" movie series required a lot of green screens. And, in at least one case, green gloves.
Let's look at this scene from "Harry Potter and the Half-Blood Prince," the sixth movie. While Hermione is chatting with Harry, she's also replacing books on their shelves in the Hogwarts library. Instead of placing them directly on the shelves, the books float back into their place and slot neatly on the shelves on their own.
How'd they do it? The books themselves aren't animated; they're totally real. Instead, it looks like there were people standing on the other side of the shelves with green gloves, which were blended into the background during editing.
It's a big jump from "Harry Potter and the Sorcerer's Stone," where Harry had to fumble around with books in the library's restricted section in his search for information about Nicolas Flamel.