I applied Hartz Ultraguard Pro to my cats yesterday. One had a terrible reaction. Apart from it turning into a big oily mess on the back of her neck, she got extremely vocal. I was tending to another cat and turned around and she was staring at me drooling. I scooped her up and her skin where the product was at was hot to the touch. I immediately washed her with Dawn dish detergent. Once dry, she seemed to be fine. No telling what would’ve happened if I had left it on there. I called the Hartz number from the package and reported it. Although they were friendly and acted concerned and apologized, no one offered to give me my money back. Wal-Mart isn’t going to take back a half used package, even with a receipt. After finding this site, I guess I just need to be grateful it didn’t kill her. I am. Lesson learned.