The dog leash is a shock absorber and creates a cushion from any sudden moves made by you or your dog. As you encounter your dog's pull, the Bun-Gee Pup-EE leash stretches and the resistance your pet experiences teaches them not to tug anymore, helping you to train your dog! A GREAT Restraint System! Even if your dog doesn't play tug-a-war, it still looks terrific and functions perfectly. Your dog's weight determines which size you need.