We adopted our 4 yr old heeler in January and got him in to the vet right away for his first check up. He got a clean bill of health and the vets even remarked that he was incredibly healthy for a dog who had been abused by previous owners. A few weeks ago, I saw him scratching a lot and thought maybe I should get him a flea collar, just in case. When I was a kid, we always bought the Hertz collars, so I didn’t think twice about buying one for Herbie. When I read the instructions (Wash hands thoroughly after touching…do not touch your eyes after handling…call poison control…) I was a little concerned about putting what amounts to a pesticide on my dog, and decided to watch him closely for the next few days. Within a few hours, he seemed lethargic, but he’s not high-energy so I didn’t think it totally out of character. The following morning, he began vomiting yellow foam. That was enough to convince me to remove the collar. Within hours, Herbie was better and by the following day he was completely recovered. I decided to do some research to see if others had similar problems, and stumbled upon this website. Wish I had seen it sooner!