Cat hair and FLEAS. Because the flea treatment I gave them last month didn't work, and I didn't realize what was happening/snap out of denial until significantly later than optimal, so now I have to hope their second treatment holds while I daily vacuum everything over and over for weeks. I have a cordless vacuum but its battery runs down fast, and a mediocre corded vacuum that's over 10 years old with a stiff/brittle cord and gets dust everywhere when emptied. This new one is gonna be my best friend for several weeks while I treat the whole house, and wait 3 more weeks to give the cats their next dose of a a different treatment that should be more effective (but I have to wait for their latest treatment to wear off so I don't overmedicate/poison them). I haven't seen any live fleas since I dosed them Sunday, and I'm hoping that between i carpet powders, household flea sprays, and vacuuming vacuuming vacuuming, I will never see them in here again.