Forget virtual reality and digital interactivity -- what makes this print ad, created for the Ford Explorer, really interactive is that it's a good old-fashioned optical illusion. The poster challenges you to park a "ghost" car in the picture with only the outline visible. The copy orders you to: "Stare at the dot in the car for 30 seconds, move your eyes to the empty parking space. See how easy it is to park." People who follow these instructions will find themselves looking a shadowy car shape that they can "park" between the other two. The ad was created by Israel's BBR Saatchi & Saatchi.