I grew up in France in an era when it was very common to take temperatures rectally, even for adults. Back in those days, people of course used glass thermometers, with mercury or some other product inside (I think some had colored alcohol, some gallium, I was too young to know about the details). Mom waited for 3 minutes (though I recall a thermometer said “maximum à la minute”, so theoretically it should have worked in one minute).
These thermometers had a thin tip, and then a thicker part (like a little finger). You inserted the tip but not (normally) the shaft. They could be used orally or rectally, or even under armpit (but my mother considered other methods than rectal to be unreliable, so…).
I knew old-style American rectal thermometers were different but never had an occasion to see any (by the time I was living in the US and paying attention to medical glass thermometers, there were still “oral” vs “rectal” glass thermometers but these seemed to be only color variants on the same European-style design).
I therefore did not understand remarks by Americans that their mother would detect constipation or mention waste in the rectum if the thermometer came out dirty. I mean, a European thermometer tip does not go deep enough to encounter waste unless the patient is really close to defecating (I know my mother used the thermometer to stimulate my anus and trigger a bowel movement when I was little…).
It took me a while to think about the following hypothesis: an American thermometer is thin all the way, so may have the tip inserted much deeper than a European one. It may realistically encounter waste.
What do you think? Is this reasonable?
This would not explain the "constipation" diagnosis. However, encountering waste, especially if the child has been told to go potty when feeling like it, may be a sign that he or she is "withholding".