My cat had fleas and I wanted a quick over-the-night fix. I went to WalMart and purchased a Hartz flea collar. Immediately after putting it on my cat she started breathing very heavily, coughing and running around like crazy. She had the WORST reaction to it and had major scabbing and hair loss on her neck. It is so sad that this company is still in business after the thousands and thousands of animals that have been made victims by their disgusting products. :(. My cat is thankfully okay and recovered. However, the vet was very adamant about not letting any of her patients use any Hartz products on their animals.