My husband & I ran out of the Advantage that we usually give our cats and we happened to be at a store that sold Hartz Flea & Tick Drops. We applied the drops to the cats late Thursday afternoon & by 10 o’clock Thursday night violent fighting erupted amongst our three normally docile, fat, lazy house cats. Hair was flying, bodies were slamming into walls, they were growling & making horrible gutteral noises – basically they were trying to kill each other. The fighting continued off & on through the night and by Friday morning, one of the cats had jumped through a 2nd story screen window. That was 3 days ago and we haven’t seen her since. And our 2 remaining cats are still fighting and trying to kill each other. These are 2 cats that were brothers from the same litter and have been together for 11 years. Upon trying to find a website to contact Hartz, I came upon your site (and several others). We had no idea. Hartz seemed like a reputable pet brand name. It’s a crime that they’re allowed to continue to sell these products.