My cat Mack does this too. Since I have 4 cats I wasn't sure who was doing this until I saw him do it. Usually he puts twist-ties in the water bowl. I really don't know where he finds them but occasionally one will be in there. He also puts the toy mice in there at times. I worry about the twist-ties being in the water dish because I have one large water bowl for the cats and the dog drinks out of it too. I am afraid Casey will accidentally swallow one. I used to have separate bowls for the cats and dog but the cats always ended up drinking the dog's water so I just give them one huge bowl now. Anyway, I read that they view their water dish as a safe place.