Yes I know about serotonin etc, but why does the stimulus of petting a fluffy critter evoke that response in the first place?
My personal uninformed armchair theory: We’re apes, and apes pick bugs out of each other’s fur to bond as a group. But when our ancestors forsook the trees for the plains, we shed our fur to gained sweat glands in order to become the ultimate persistence hunters. Yet the urge to groom remains. We have no fur and we must pet.
I have not been able to find this again, but I swear that I once read a study where they had measured oxytocin levels while stimulating a badgers nipples. I just want to see the person who did this. Anyways, it worked as expected, and they had some data on which frequency worked best. Iirc it was one slow stroke every 1.5 seconds. Which is kind of the pace I pet cats to relax.