What's the fastest thing on Earth?

Four men are being interviewed as part of a scientific survey that is being conducted in order to determine what's the fastest thing on earth.
The first man says,"I think that it's probably a blink because you can blink so quickly that sometimes you don't even realize that your blinking."
The second man scoffs at this idea and says,"A thought is certainly much faster than a blink, and I challenge anyone who disagrees with me to speak up now!"
The third man thought on it a moment before replying,"I have to agree that a thought is faster than a blink, but I'm afraid you're wrong. You see, electricity is ten times faster than both of those things. When you flip a light switch the light turns on instantly. You don't even have time to think about how it gets from the power company, and all the way down miles of power lines to your house, through your fuse box, to your light switch, and finally to the light turning it on."
The other two men thought that this was a pretty convincing argument, and so the three of them agreed that electricity must be the fastest thing on earth.
Then the fourth man says,"I am sorry, but all of you are wrong. The answer is diarrhea." The other men laugh at him and ask,"are you crazy? How could it possibly be diarrhea?!" To which the fourth man replies,"I can state with certainty that the answer is indeed diarrhea! You see, just last night I woke up in the middle of the night with a case of the squirts. Before I could blink, think, or turn on a light I shit my pants on the way to the bathroom!"