Hi! I took in some stray cats a few months ago, they were given flea treatment once so far by the rescue. One was given Revolution(luckily. she was also the one most infested with fleas at the time) while the other two were given Zodiac. But Zodiac was so soo greasy and spread across their backs so I ended up cleaning the treatment off in about 2 days because I was worried they would ingest it. Now it's been a few months, I can still find little dots of black all over my furniture where the cats are active, I even started finding little dots of black in my own cat's fur, who had no flea problem before. However, these little dots of black don't move. I assume they are dead fleas or flea poops? I test combed all the cats with a flea comb and didn't find any live fleas either. Should I still do another round of flea treatment? Is it normal for them to have these black dots falling off of them a few months after flea treatment? (the only one unaffected in this and remains pristinely clean is the one treated with Revolution) Thanks!