Find the right combination

An office manager was given the task of hiring an individual to fill a job opening. After sorting through a stack of resumes he found four people who were equally qualified. He decided to call the four in and ask them one question and their answer would determine who would get the job.
The day came and as the four sat around the conference room table the interviewer asked "What is the fastest thing you know of?" pointing to the man on his right.
The first man replied "A thought. It pops into your head. There's no forewarning that it's on the way, it's just there. A thought is the fastest thing I know of."
"That's very good!" replied the interviewer. And now you sir?
He asked the second man. "Hmm.... let me see, A blink! It comes and goes and you don't know ever happened. A blink is the fastest thing I know of."
"Excellent!" said the interviewer "The blink of an eye. That's a very popular cliché for speed." as he turned to the third man who was contemplating his reply.
"Well, out at my dad's ranch, you step out of the house and on the wall there's a light switch, when you flip that switch, way out across the pasture the light at the barn comes on in an instant." Turning on a light is the fastest thing I can think of."
The interviewer was very impressed with the third answer and thought he had found his man. "It's hard to beat the speed of light." he said. Turning to the fourth man, he posed the question.
"After hearing the three previous answers, it's obvious to me that the fastest thing known is diarrhea."
"WHAT!?" said the interviewer, stunned by the response.
"Oh I can explain." said the fourth man. "You see the other day wasn't feeling so good and I ran for the bathroom. But, before I could think, blink, or turn on the light, I'd crapped in my pants!"
He got the job.