"A pensieve. It holds your thoughts when you've got too many." There's an image of Harry looking into a different pensieve in another room, an impression of the sharp, gritty taste of candied pineapple, and then the memories fade into a murky, grey-green as the surface stills. "If you're a skilled wizard, it's possible to pull out and put aside things you need to know, but don't need to have on hand. A good way to share information quickly, too."