If you grab just above the base of the tail with your hand (palm side on the underside of the tail) and then turn your wrist 90 degrees pushing or pulling, depending on the situation/angle/comfort of the person the tail towards the head firmly, but not so hard you are in danger of causing injury to the tail. Still, the pressure has to be pretty hard. This pressure pinches the spine or a nerve and seems to distract the animal but when you are castrating one with a knife in addition to seeming the keep the soon to be steer still and less squirmy it also appears to have some epidural action because we have cut many with a proper tail pinch that have stood like champs. Maybe someone else has a better explanation. But you must grip at the base of the tail or near it and push the tail forward, NOT lower on the tail because then you can break the tail with the pressure.