Daniel drops his fruit bar on the floor and picks it up.

He invokes the five-second rule.

Mom takes it away.

The five-second rule says that if you pick up dropped food fast enough, it is safe to eat -- because bacteria need time to transfer from the floor to your food. Get there in under five seconds and you win.

In 2016, a food scientist named Donald Schaffner at Rutgers University decided to actually test it. His team dropped food onto contaminated surfaces thousands of times, measuring bacterial transfer at different contact times. The findings were not good news for the rule.

Bacteria can transfer in less than one second. There is no safe window. The moment food touches a contaminated surface, transfer can begin. Time does matter -- longer contact means more bacteria -- but there is no point at which the food is  ...