fastest thing?

The other day four guys were just sitting around, shooting the bull. One of them asked, 'What is the fastest thing you know of?'
The first man replied, 'A THOUGHT.' It just pops into your head. There's no warning.
'That's very good!' the others said.
The second guy said 'Hmmm...let me see 'A blink! It comes and goes and you don't know that it ever happened. A BLINK is the fastest thing I know of.'
'Excellent!' everyone said.
It was the third guy’s turn. '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 on the barn comes on in less than an instant. 'Yep, TURNING ON A LIGHT is the fastest thing I can think of'.
Everyone liked that one, too.
The final man thought for a moment and said “'After hearing the previous three answers, it's obvious to me that the fastest thing known is DIARRHEA.'
'WHAT!?' everyone else said.”How can that be?”.
'Oh sure', he said.. 'You see, the other day I wasn't feeling so good, and I ran for the bathroom, but before I could THINK, BLINK, or TURN ON THE LIGHT, the diarrhea was there!
'