Martingale collars, or limited-slip collars, are designed to prevent dogs from slipping out of their collars without choking them. They tighten gently when a dog pulls on the leash but have a built-in safety mechanism to avoid too much pressure on the neck. These collars are particularly beneficial for dogs with slender necks relative to their head sizes, such as Greyhounds, Whippets, and other sighthounds. The design ensures the collar tightens enough to prevent escape, making it a safe and humane choice for securing these breeds during walks.