Now that I think about it, I use my toe for a bath, arm for a shower. Same principle, though. This woman must have rocks in her head or chemicals in her bloodstream.
Having a handheld shower head fed off of a bathtub spigot diverter, my first test is under the spigot and the second test is out of the shower head after diverting, both cautiously with the hand. If the laundry machine or dishwasher kicks in with a fill during my ablutions, the water gets suddenly cooler. I cautiously readjust to a comfortable level, keeping in mind that when the machine fill ends I will get a burst of hot water again and that I have to be alert for that. There are new nanny state required temperature equalizers that my county code now calls for in new bathroom installations, but I’m grandfathered. Were I to have houseguests that are elderly, ill, or very young I would change the valve (with some regrets) to avert possible injury. This change would also mean I could not get maximally hot water out of the bathtub spigot, which I occasionally want for household cleaning purposes.