You or someone you know has probably made the claim that it's OK to eat food that falls on the ground if it's picked up in less than five seconds. That chocolate chip cookie that slipped out of your hand? Totally cool to eat off the ground because it was just there for three seconds. That last bite of sandwich? It was only on the ground for two!
Is that how the transfer of bacteria actually works? As it turns out, the answer is a little more complicated than you might think.