I have a 13 year old domestic shorthair cat. Over he last two days, she's had loose green-gray stool on floor (not in the litter box). She _has_ urinated in the litter box. She's an indoor cat though we do have a dog that goes outside. We also recently changed her food from one brand of dry food to another but we've never had this problem before when the food had been changed.
She is still eating her food but she's not a social cat--mostly she onely comes out to eat and use the litter box--so I don't know if there are other symptoms or not.
Any thoughts on what might be causing it? Is the food the likeliest cause or something else?