One of my cats Maya does the same but with metal bottletops. She has them all in a big empty flower pot, and when she wants to play she takes them out one by one and goes around the house meowing like mad. It actually sounds like someone is torturing her, I would not be surprised if one day the neighbours call the animal welfare unit! Maya wants someone to play with her and she will go on meowing until someone takes pity on her and throws the bottletop. THen she will run after it, but will take it back only if she feels like it. We find those things everywhere: under the furniture, in the beds, in shoes in the her and in the other cats' foodbowls and litter. Not very pleasant if you walk on them barefooted in the middle of the night!