What's the three second rule?
Scientists are trying to discover what happens to food when it drops on the floor for a short amount of time.
Some people think that if you drop food and pick it up within a three seconds and dust off the dirt, then you can munch away without the risk of germs.
Though it's not a good idea to drop any food on the floor, scientists at Manchester Metropolitan University have been testing the theory out to see whether there is any truth in it.
Ricky's been to find out the results...