I learned about Hartz years ago. Rusty was about 4 when I used Hartz flea spray on him. By morning, he was vomiting and shaking. Instinctively, I stuck him in the sink and started washing it all off of him, and had my husband get on the phone and try to find the vet (it was a Sunday). His service finally found him on the golf course. He called and told us to get to his office as quickly as possible. His wife was waiting with the door open when we pulled up. The doctor injected him with the antidote before I could even put him down. He said Rusty was literally moments away from dying, and washing that off of him was the only thing that bought him those few extra minutes. I was confused, because Hartz had been around forever, and I thought it was a trustworthy brand. My vet explained that over the years, fleas have built up immunity to the pesticide used in common “supermarket” brands. Rather than spend big bucks on research and development of a new pesticide, these companies just increased the amount in their products to keep them effective. Afer 4 or 5 decades of this, the formulations are so concentrated, they are as likely to kill your cat as the fleas! That year alone, my vet said he had lost 4 other cats that way, and treated many others. His advice was to never use anything but Frontline or Advantage for cats. It cost my entire Christmas savings to pay the bill, but of course I did not hesitate. I wrote Hartz a strongly worded letter with copies of my receipts showing when and where I bought their product, and my resulting vet bill. They sent a check to reimburse me, but there was a clause on the back saying that by cashing it, I was releasing them from any furher liability. If I knew then what I know now, I would have filed a law-suit and turned my experience into a media circus!