I have posted this before, but I think it is worth re-posting. The size and shape and smell of your stool indicates what the inside of your lower colon looks like and how well your body is.
A healthy adults's stool should be the length and width of a small infants arm.
It should be a nice shade of brown - this indicates that your liver is functioning like it is supposed to - bile produced from the liver is green, which mixes with waste - this results in the brown color. If the stool is consistently pale colored - this is a sign of liver problems. It is actually one of the first signs of cirrosis of the liver.
The stool should sink to the bottom of the bowl. This tells you that you are not eating too many fats and that the liver is breaking down cholestrol like it is supposed to do too. Floating stool is a sigh of too many fats in the diet and/or liver problems. The bile from the liver breaks down fats and cholestrol and helps remove them from the body.
The stool should have a round shape that is a couple of inches thick in diameter - very small pencil-thin stools indicate build-up on the colon walls. The stool is coming through "the hole of the doughnut" so to speak. Very thin stools can also be a sign of colon tumors. One note here - the size of the lower colon depends on the size of the person. A small 100 pound female will, of course, have smaller stools than a male 350 pound linebacker :)
And last, but not least - healthy stool should have a not unpleasant odor. No air freshener required :) Very foul stool indicates toxins in the body.