It is false. They did an experiment on the five-second rule on the TV show Mythbusters. They dropped various items on the floor for different lengths of time. It was shown that the amount of time the food was on the floor was not a factor. It picked up enough bacteria to be potentially harmful the very moment it came into contact with the floor. The variables that made more of a difference were the amount of moisture in the food, the surface type of the floor, and what conditions it was being dropped on. Moist foods picked up more bacteria than dry. Obviously, a dirty floor passed me bacteria than a clean one.