What does it feel like? This is all my opinion on it. To me, it all depends on the thermometer that's being used, along with the lube, or lack there of that's being used. As a child, I distinctly remember my mom taking my rectal temp with a standard, non pear shaped glass thermometer. I remember her putting it in, the feeling of it in there, almost moving in and out slowly as she held it in place, and then the removal. It was always almost a ticklish type feeling with any of the movement that may have been happening "back there". Today, I have a multitude of thermometers that I like to use when taking my rectal temperature. I will always be a fan of the traditional glass thermometer, but as an adult, there is almost no feeling to me what so ever when I have one inserted. I have an older B-D non flexible digital that's got the red cover on it, that one i'm not a big fan of, it's very rigid feeling and not while it doesn't hurt, it's not comfortable. I've got a red model Geratherm thermometer, that one used rectally is pretty comfortable, you can definitely feel it when it's inserted past the shoulder. I will have to say my current favorite, as far as feeling goes, is my Filac Fastemp thermometer. The probe, when inserted is just the right size to me, and it's got almost a heavy feeling to it, likely due to the cord, when it's inserted. As I said, the traditional glass will always have it's place, especially for the visual aspect, but for me, right now, the digital probe feels the best.