A tight pinch of skin between thumb and forefinger is a useful skill in a variety of circumstances. It requires no tools, can immobilize or quiet some horses for a short time, and can be used to distract an unruly horse while performing a treatment or short procedure. It probably causes an endorphin release in horses. Endorphins are natural pain killers that exert a calming effect.
A shoulder roll (grabbing a handful of skin at the shoulder and “rolling” it tightly against a horse’s body for a short time), is particularly useful for giving IM injections to young horses and to horses that resent injections (needle shy).
However, like a nose twitch, in some horses these methods of restraint are not effective and may even be counterproductive. You, with the guidance of your vet, must determine whether this skill may be appropriate to perform on your horse.
Halter your horse. Use your dominant hand to grasp a handful of skin in front of (cranial) to the shoulder. Your thumb should start pointing toward the head of the horse.
Squeeze as tightly as possible, making a fist with the horse's skin within it, now roll your thumb back toward you, move your elbow and body toward your horse’s shoulder, creating another level of torque on the skin.
Tips for safety & Success
It takes a moment for the endorphin release, so wait until you see your horse relax before performing whatever procedure you plan to perform.