Is it true that there are nerve endings reaching from the butt to the clitoris, and that's why spanking's supposed to feel good? I'm skeptical.

Ah, the joy of a good spanking - the sting of the lash, hovering between pleasure and pain, the warm rush of blood, followed by the swell of orgasm… You can see why spankings are popular with some people. But they’re not everyone’s cup of tea, less about pleasure and more about pain and humiliation. Yes, there are physiological reasons why a spanking can feel good: 1) there’s a sympathetic stimulation via the nerve roots to the other nerve branches in the pelvic floor; and 2) the same neural circuits are often activated either by painful or pleasurable stimuli - but it’s definitely more about the psychological.