We've noted that babies can already make some predictions about where an object will reappear once it vanishes from sight. For instance, if you show babies a rolling ball that disappears at one end of a screen, they predict that it will reappear at the far edge of the screen at the right time. To do this, babies have to be able to think about the object even when they can't actually see it. Another way of testing this capacity is to show them a sort of magician's trick. Suppose you show young babies the object disappearing behind the screen, and the object fails to reappear or show up in an odd location. Babies in the first six months of life look at this sort of scene for much longer than a scene in which the object reappears where it should.