Higher math

Just one sharp smack - on my inner thigh - but an hour later I can still feel it burn. We'd been in bed talking about all the chores that need to be done to today and then SO leaned over, said "up you get then" and whack - palm meets thigh.

And I'm not talking sit-spot. No, it was inner thigh and well out of the spank zone. Wow, did it sting. My squeal was louder than the smack itself and would have been heard by our youngest, if she wasn't locked in her bedroom playing europop as loud as she can get it.

So my question is, why does all this not add up? Why does moving the impact about 10-15cm south of the usual target zone multiply smart so much?

I reckon I'd rather take 50 spanks to my behind that a couple to inner thigh. Why is one so much stingier than the other? Is it some fundamental difference of skin structure? Is their a dermatologist out their with spanko leanings who can answer this question?