Penny is on Sentinal and we suddenly noticed the fleas FLEAS last week. We have the cat on Advantage (indoor cat) and we have all wood floors that we have been cleaning like mad. Penny must have picked them up outside - but shouldn't the Sentinel work on those? She has been on it for 5 months. I went to the vet and got her some Frontline and the first dose yesterday did nothing - the fleas didn't even look ill. I thought maybe I had gotten it on her fur rather than her skin so I gave her another late last night. She is still itching like crazy. It is making me so sad to watch her. Any advice? What else can I do?