I bought the Hartz flea collars for my babies. Within a couple hours of putting them on, the first one started stumbling around and acting really funny. I immediately yanked them off and bathed them in dawn. It took a few hours but they started doing better. My husband didn’t believe that’s what it was and put one on one of them a few weeks later. A couple hours later, THAT ONE was acting funny. He removed it and pulled the rest out of the cabinet and threw them all away. We will NOT buy anything else from them.