Tldr : human, & dogs are mammalian creatures. Simply said our body has a range of normal temperature, unlike snakes.

When you have bacterial, viral, fungal infection (yes, unwell) the first thing most bad organism do is to mess up with this control (infection comes, your body fight back, epic war happening in your body, internal nukes, gilgamesh style, yidi yidi yada) so you become feverish.

How to test fever? Well we use to have those mercury thermometer since it was the most accurate back then, now we have better ones. But problem is, with evaporation, physical thermometers cant detect temperature accurately (physics101, you know, conduction, wet bulb effects, evaporation effect) .

The anus, being literally inside you, has the most accurate body temperature (minimal effect of conduction) .

Now we have those infrared thermometer. They are cool since it can detect surface temperature well. We cant use it for dogs since they are too hairy & babies since their surface area is small. But its ok for adult

I know you love bitcoin, and you hate doctors, but please at least, spread facts