Awww...cats will do strange things. My cats don't bother our clean socks, but Little One will pick up a dirty sock and carry it in her mouth with it dragging behind her and sleep with it like it was her security blanket.
Now, when I was growing up, our dog used to EAT dirty socks, so this is an improvement.
Maybe she meows at it to get it to play with her.
Oh, and my cats LOVE bottle caps too! Anything that makes noise while being batted around is their idea of heaven. Try tearing off tin foil and roll it into a ball. Mine go crazy for them!