Who hasn't done this: You drop a piece of food on the floor, pick it up within five seconds and pop it in your mouth. It's still okay to eat, right? Not exactly. According to a recent survey, women are more likely to invoke the "Five Second Rule" than men. Not surprisingly, everyone's more inclined to eat a dropped cookie than a dropped piece of broccoli. But is it really okay to eat something you dropped on the floor? Well, there are a few schools of thoughts on this.

First, at the University of Illinois, floor tiles were purposely contaminated with E.coli. Then researchers placed cookies and gummi bears on the tiles for anywhere between one and ten seconds. The upshot was: Almost-instant food-poisoning. 

But a new study was done at the University Chicago and University of Iowa. Researchers tossed gum, cookies, chicken legs and hot dogs on different types of floors. They found the safest surface is the kitchen floor. Only the hotdog was contaminated enough in five seconds to make you sick. The living room carpet isn't quite as clean. Both the hot dog and the chicken leg were contaminated within five seconds. And basically, anything you drop on the bathroom floor or the lawn is a germ-freak's nightmare. Every item that fell on those surfaces was contaminated enough to make you really sick.

Want to know who the first person was to invoke the Five Second Rule? Experts say it was Genghis Khan, but he used a "20 Hour Rule." And anything that had been lying in the dirt for less than 20 hours was still safe to eat. So if you drop a cookie on the kitchen floor, go ahead and eat it within five seconds. Chances are good you won't get sick. But if you're at a picnic and drop any food on the grass, toss it out!

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