"The 30-Second Rule, A Decision Tree" by Audrey Fukuman and Andy Wright
I think it's more like the 3 second rule because eating something that has been on the floor for 30 seconds is rather frightening... but I'm not judging.
The flow chart was in an article titled, "You Dropped Food on the Floor. Do You Eat It?" Do I eat it?! I don't need to consult a decision tree because the answer is so simple: always eat it - ALWAYS! (this rule especially applies to medium rare cheeseburgers and all things containing chocolate).