I found some slut's wool under the sofa while cleaning.
slut's wool
idiomAccumulated dust, fluff, hair, etc., that tends to occur indoors in areas not regularly dusted, such as under heavy furniture.
Origin
disputed originFrom slut (“a slovenly, untidy person (archaic)”) + -'s + wool.
She moved the heavy wardrobe and discovered a thick layer of slut's wool gathering in the corner.
The neglected attic was filled with cobwebs and clumps of slut's wool that had accumulated undisturbed for several decades.