It works by stimulating the vomiting reflex (throwing up from stomach). This collar is a pain-free alternative to teach the dog to release the bite on command. It works well despite fact that the dog is in drive or in strong positive stress, e.g., very committed to attack the helper he is transporting. When the Spit-Out collar is used (bringing "unpleasantness"), the dog's vomiting reflex is stimulated. Instructions for using the Spit-Out collar The collar is put far forward on the neck, in front of the "Adamís apple." Then one tightens the collar so it stays on place. Note: do not tighten too much, because if a dog is in drive and barks at the helper, this can also stimulate the vomiting reflex. Tighten only so the collar stays in the right place. Hand made in our saddlery in Arlöv, Sweden. Topp quality work and material used. Black color.