Whenever my son drops food on the floor, he wants to eat it. I discourage him from doing so, but he invokes the "5-second rule" and says that food is safe to eat if you pick it up 5 seconds or less after it has hit the floor. Is that true?
No, it's never a good idea to eat food that has been dropped. The 5-second rule is just wishful thinking — bacteria can attach to food as soon as it hits the floor. And foods with wet surfaces, like an apple slice, pick up bacteria even more easily than, say, a cookie.
The longer the food is on the floor, the more bacteria it will accumulate. But even food that's picked up quickly can be contaminated if conditions are right. While visibly dirty floors are obvious hazards, those that look clean also can harbor bacteria. Some germs can survive on floors for a long time, and without a powerful microscope it's impossible to see them.
So what are you to do with that delicious piece of whatever that just slipped from your grasp? The safest choice is to throw it out.