I honestly believe that most issues that horses have with twitching comes from improper or excessive twitching. You are not supposed to pinch them hard enough to inflict pain to release the endorphins. The locations where twitching is most effective (lips, ears, side of the neck) are pretty sensitive areas on a horse because of the concentration of nerve endings. You squeeze just hard enough to excite the nerve endings a little bit, not hurt them. It is kinda like massaging the meat of your hand between the thumb and first finger when you have a tension headache; to most horses, it actually feels really good. I still don't like the ear twitching because it is misused so often and creates headshy horses; that is a very sensitive button only to be used in the most extreme of circumstances, IMHO.