My cats will also eat things that they're not supposed to. My girl Pearl will also elastic string and one time I was scooping the box just after she had used it and there was something red in her poo. At first I thought that it was blood but it was a red elastic string that she has eaten from a cat toy that my mom had given to me. Thank god she passed it. I didn't even know that she had eaten it so I can't tell you how long it took her to pass it. I found the toy and threw it away. I hope that your cat will also be able to pass this. Now I'm very careful with what I give my furkids to play with. I even cut off the tails of the mice toys that I give them just to be on the safe side. Good luck.