I used a Hartz flea collar on my cat. A day or 2 later when I was petting her I noticed her neck looked funny. When I took her flea collar off I seen her fur was missing halfway around her neck and the skin was raw. I called the vet who told me to wash her neck off and throw out the collar. I was mortified and contacted the company. They offered to give me coupons to replace the collar. I told them they were crazy, not only would I never use the collars again but wouldn’t use any of their products and they could keep their coupons!