I remember being fascinated with thermometers from a very young age. When I was growing up (in the late 70s and 80s), every doctor visit began with height, weight, and temperature. On the doctor's table were two metal or plastic cylinders, clearly labeled "oral" and "rectal", with two thermometers sticking out of them. I watched with apprehension as the nurse (who wore a white uniform with stockings) chose a thermometer. At least within the recall of my memory, she always chose the oral thermometer, though I suspect that my fascination started earlier when that wasn't the case.
By the time I was 12 or 13 the fascination was deep seated. I remember distinctly how I graduated to the "teenager" section of my doctor's office, which had its own waiting room and exam rooms, and my mom wasn't allowed to come back with me. As I waited for the doctor, I looked at the table, and sure enough, there were both oral and rectal thermometers in this exam room, too. I couldn't contain my curiosity. I looked at the red-tipped thermometer sticking out of the "rectal" jar, then picked it up and held it in my hand. I can only imagine what would have happened if the doctor had walked in at that moment - or if I had dropped it on the floor and broken it! Alas, I put it back in the jar, and it never found its way into my rear end.
And then, sometime in the late 80s, the doctor's office got an ear thermometer, and they hired a young nurse who wore blue scrubs instead of a white skirt. It just wasn't as much fun after that.
There's one more detail that's important to me. Whenever the nurse took my temperature, she put a plastic sheath on the thermometer (B-D Temp-Away). (I remember the school nurse doing this, too.) There was a blue box of oral sheaths and a red box of pre-lubricated rectal sheaths. I almost never see plastic sheaths depicted in images or stories these days. The fluted edge of the sheath gave a nice tickle to the underside of my tongue. These days I can only find the sheaths for digital thermometers, which tend to have a sharp seam on them and just don't feel right.