Characters might enter a room and see the rough stone walls, the upturned chair, and the heavy table. But would they be likely to see the scratches on the floor made by the secret door or the dark smear of blood on the chair? If a character searches these areas, the scratches and blood will be found automatically, because they are not hidden. However, the gamesmaster can give players a chance of their character just noticing these features, even without conducting a proper search.