A few minutes ago I was cleaning the litterboxes and found in 2 of them, some very runny stool with a little blood in it. Im very concerned! I have 3 cats and all 3 use all the boxes. I have no way of telling which cat it came from and not only that, all 3 seem their normal selves and healthy and playful just like normal. Is this something that can just happen occasionally maybe from an upset tummy or something they ate that didnt agree with them? Or should I be really concerned? It just started because when I cleaned the boxes yesterday everything was normal. What should I do??