We all have our rules.
For some, it's five seconds. For others, ten. And for students, it tends to be measured in days.
Every time we drop food on the floor, we know we're taking a risk by picking it up again and putting it in our mouths. But, well, it's food. And it wasn't there for that long.
A microbiologist took it upon himself to test just how dirty food gets when dropped on the floor.
Anthony Hilton of Aston University in Birmingham, UK, thought it might be instructive to try various surfaces to see if what goes down can come up again intact.
He and his students dropped toast, pasta, and sticky candies on various floors -- carpet, laminate and tiled surfaces -- for between 3 and 30 seconds. Then they ate them. No, wait. Then they examined them for bacteria.
Given that this research was happening in my own hometown, I worried for the results.
What Hilton and his students discovered is that the five-second rule might be appropriate. The longer food stays on the floor, the more likely it is to attract biological nasties.
Interestingly, though, they also discovered that different surfaces had different levels of risk.
Hilton said: "We have found evidence that transfer from indoor flooring surfaces is incredibly poor with carpet actually posing the lowest risk of bacterial transfer onto dropped food."
I find this shocking. I have seen carpets (in Birmingham and elsewhere) that defied definition. It was as if a carpet had become one wide, green piece of bacteria. Surely, then, it depends on the state of the carpet.
I thought that everyone had, at one time or another, picked food off the floor and eaten it. It's either because the food is so good or the eater is so hungry.
However, Hilton's research discovered that only 87 percent admitted they would eat food off the floor or had already done so.
Naturally, I don't condone conducting this experiment on various floors in your home. I have a feeling, though, that I may not be able to stop you.