Sacking out is a method used by horse trainers to desensitize a horse to potentially frightening situations or objects.

An example of such an object might be a plastic bag suddenly blowing across the path of horse and rider, which, if the horse has not been properly desensitized, could result in spooking. Spooking is potentially dangerous, as it can result in fallen riders or horses bolting into traffic. A typical method to desensitize the horse to such an object is to tie a plastic bag to the end of a stick and, through multiple sessions, slowly get the horse used to the object. The sessions would likely include waving the bag in the air, rubbing the horse's body, face and legs with it, and ultimately whipping the bag against the ground near the horse's feet.

The term, "sack out", also refers to going to sleep.