The rule states that there is an illustrated time window where it is innocuous to pick up food after it has fallen onto the floor and come in contact with the germs.
Its origin is not clear, and there is no scientific theory behind the rule.
Based on this rule, the food comes into contact with some microbes only when it is dropped on the floor for a lesser time.
However, the extremity of contamination depends upon the type of surface and the texture of the food.