Have you ever dropped food on the floor and picked it up to eat it? Clark sometimes thinks it’s OK for parents to let their kids do this because it builds their immune system. There's the five-second rule, which holds that anything on the floor for five seconds or less is OK for human consumption. Yet the FDA says that the five-second rule is bogus. Meanwhile, The Washington Post reported that if the fallen food in question tastes good -- like a cookie or piece of cake -- people will even push it to 15 seconds! But stomach aches and other intestinal distress can be associated with this practice, so be careful. The book answer is that it's not a good idea to eat food off the floor, but people probably won't be changing their ways anytime soon!