Yesterday, as I was on a training run I realised I needed to defecate. It was fairly uncomfortable - using a phrase favoured by a friend, ‘the turtles head was poking out’ - but the public toilets on my route were locked.
When I returned to my car, and started driving to my next appointment (where a toilet awaited) I started farting.
Large farts, but without the sense of pressure that I experienced while running - in fact, releasing the farts allowed me a sense of comfort for the 20 minutes or so it took to drive to the destination.
Along the way, I was struck by the observation that flatulence usually (in my case, at least) precedes the need to defecate - aside from the unfortunate phenomenon known colloquially as “sharting” wherein a fart is accompanied by a number 7 on the Bristol Stool Scale
So why does the gas precede the solid? I would expect the gas/solid to be fairly evenly spread throughout the colon, with peristalsis moving both at the same rate.
Once I did get to the toilet, my deposit (a number 4 on the Bristol scale) was accompanied (as I would expect) a large amount of gas, fairly evenly spread throughout the experience.
What then causes the initial gaseous build up? (I mean, the large reservoir of gas that precedes the main event - I know what actually creates the gas)
As a bonus answer: aside form the aforementioned sharting, how come most people are able to discern and release a fart, without releasing a turd? The sense of pressure is the same, but somehow I know that I am doing a fart, when I am doing so, rather than soiling myself.