Who hasn't picked up a piece of dropped food from the floor, given it a quick blow and assumed it was still safe to eat? To many of us, it is second nature to apply the age-old pseudo-scientific 'three second rule' on such occasions, telling ourselves we're safe if the food hit the floor only momentarily. The idea that food is not contaminated if it is retrieved quickly has been believed for many years - but there has not been extensive proof that this is the case.