Gross, but simple!!
Hard, Sinks....
Why they ask is this...
if it's soft, the enzymes aren't enough to absorb the nutrients and it doesn't form.
Floats, means that there is still a lot of grease/oils in it and it will be lighter than water.
Hard, means the enzymes are working and is absorbing the nutrients.
Sinks, means that like the typically normal "one", the body had also absorbed all the fats, or generally there were no fats in there so it would allow it to be heavier than water.
Hope that answered that!! (P.S. I was often asked that, along with how many times per day. Usually about once or twice a day is normal, but I've had to use the bathroom on the average of at least 4 to 6 times, depending on the day...)