When someone tell you it is safe to eat something you dropped on the floor as long as it's been there for less than five seconds, that's a rule of thumb.

For most of us, we know that the five-second rule isn't always applicable. If you dropped your apple onto a pile of mud, you know it's not safe to eat it.

Even if you have ninja reflexes and managed to retrieve your shiny red globe the second it is in contact with the brown slimy sludge, you wouldn't be consuming it right after.