Hi! Took my dog for a regular check up last week and vet spotted what looked like flea dirt. However, as she's on monthly Advocate and the flea dirt didn't stain wet cottonwool we relaxed. However, I was aghast to find fleas tonight - 2 on the sofa and one on the dog (I stopped looking for more on her as it was freaking my daughter out - will comb dog coat through tomorrow). Is it possible that the Advocate has stopped killing the fleas, please?