Almost everyone has dropped food on the floor and still wanted to eat it. Some people apply the "5-second rule" — that random saying about how food won't become contaminated with bacteria if you pick it up off the floor in 5 seconds or less.
The 5-second rule has become such a part of our culture that scientists actually tested it. As you can probably guess, they found that the "rule" is mostly myth: Bacteria can attach to food even if you pick it up super fast. So, depending on which types of bacteria happen to climb on board, you could still get sick.
Here are two facts to consider whenever you feel tempted by the 5-second rule:
Some bacteria are not harmful. But others can torture you with miserable stuff like diarrhea. Even if there's no visible dirt on your food, you can still get sick. You just can't tell what kinds of bacteria may be lurking on the floor.
So what are you to do with the piece of watermelon that just slipped from your grip? The safest choice is to throw it out. Or let the dog have it. (And there's another thing to consider — even the 5-second rule can't get around the fact that your food may have landed right in a spot where Fido parked his butt.)