From stray bits of cat hair fuzz.
I was trying to clean bathrooms and such this morning and Millie was yap yap yapping in the back yard. I usually go out there to see what's up pretty quickly, but was busy so waited until I was finished, cringing with each yap because there is nothing worse than a dog owner ignoring their dog out there yapping. Sorry, neighbors!
I go out and there she is yapping at a bit of fuzzy cat fur on the patio. Bad cat fuzz!