A martingale collar is a specialized type of dog collar that helps prevent a dog from slipping out of their collar. Unlike traditional collars that have to be buckled uncomfortably tight to prevent escape, a martingale collar is loose and comfortable until engaged. Adjusted properly, a martingale collar never chokes, but constricts snugly to prevent escape.
A martingale collar is made with two loops. The large loop is placed around the dogs neck and adjusted to fit loosely. The leash is then clipped to the D ring on the smaller loop. When the dog tries to pull their head out of the collar, the tension on the leash pulls the small loop taunt, which makes the large loop smaller and tighter on the neck-- preventing escape.