Has this ever happened to you? You're walking down a city street and it's lunchtime, You see an advertisement on a bus showing a beautiful looking burger. Suddenly, you're starving. Now you know exactly what you want to eat for lunch. You find the nearest as your fast-food restaurant and your burger then stomach grumbles in anticipation. And the you get the food. It doesn't look anything picture that you saw in the ad. Why that?