The reason why we use martingales has been covered, but I just wanted to add to the collar fetish. Martingales are like Greyhounds. They come in all colors and designs and you can't have just one!!! Giselle only has 2, but hey...It's only been 4 months...I think 2"ers should be reserved for the looong necks or the slender, swan-like necks. 1 1/2"ers are the Looks good on every Grey, imo. Thankfully, for me, Giselle can gracefully sport a 2"er