Ali, A. B. A., Gutwein, K. L., Heleski, C. R. 2017. Assessing the influence of upper lip twitching in naive horses during an aversive husbandry procedure (ear clipping). Journal of Veterinary Behavior 21, 20-25.
When engaging in procedures that horses may find aversive, restraint methods are often used to help ensure safety of both horse and handler. Twitching is a common restraint method, but its use is sometimes considered...