One of Steve Shufton's great tricks.  (He has a lot of them, but for sheer practicality, ordinary-ness of props, and audience impact, FOBULOUS is hard to beat.)     You show two similar leather key fobs, but they have different "medallions" hanging on them as decoration and differentiation.   One is a Heart and one is a star.   The spectator can examine the fobs and see they are totally normal key holders.    She puts them both into her hand, and names either the Heart or the Star.  She names (for example) the Star.   So you remove the Heart from her hand, and place it in your hand.   Then after a magical moment, the two fobs change places -- you open your hand and you are holding the Star.  She opens her hand, and she has the Star.   Again, she can examine both.