On the internet you will find advertisements for colon cleaning that claim that an average adult is walking around with 5-25 lbs of fecal material in their large intestine, caked drily on the sides. How could you evaluate such a claim if you were not in the medical field? (I apologize in advance for this post. It just somehow needed to come out.)
(1) When you feel you have to take an enormous dump, step first on the bathroom scale. Then weigh yourself right afterwards on the same scale. How much weight did you lose? Probably less than a half a pound. I have a scale that measures in 0.2 lb increments and sometimes the scale gives me the same measurement before and after a substantial bowel movement. So the claim is that you have between 10 and 74 times more crap left inside you even after ridding yourself of some serious turds.
(2) Now go to the gym and pick up a 25 lb. weight? How heavy does it feel to you. Now pick up a 5, 10, 15, and 20 pound piece of iron. A pound of metal weighs the same as a pound of shit, so you need to get a feel for how much weight this really is. Imagine that you are carrying around the fifteen-pound dumbbell within your gut all the time. Does this seem plausible? Of you have a toddler handy you can lift him or her into the air. How heavy does the kid feel?
(3) Look at a pregnant woman. Suppose she is carrying an 8 lb. baby and the placenta Or look at a person who's 40 lbs oveweigth and carrying about 25 of it in a beer belly. Do you think your colon is carrying something of equivalent mass? Wouldn't it be as big as the uterus of a pregnant person? If so, how does the stool even pass through there? Wouldn't you die of a blockage before you got to 15 or 20 pounds? If the argument is that the matter is so compacted that it has a high density, remember again how much your elimination weighed after you did your business, remember again the relative density of metal and flesh.
(4) Now look at the advertisements again. What are they selling? How much would it cost to get your insides cleaned out? Now compare this to the price of the laxatives they tell you to use before a colonoscopy. Before you get one of these, you have to clean out your entire system, and the result is that there is nothing there. I guarantee you won't lose 20 lbs.
(5) Now think of what other mental experiments you might perform to evaluate a claim of this type. You need to balance what your own experience tells you, unbiased information, and the opinions of experts. Suppose the claim was one like "we only use one tenth of our brains." How would you evaluate a cliché meme like this? Maybe it might be more difficult with some more elusive ones.